Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $232.92   3.755%   $241.6661   $241.67   $241.65   $241.70  
  Purchase #2 $242.33   13.601%   $275.2893   $275.29   $275.30   $275.30  
  Purchase #3 $119.73   9.845%   $131.5174   $131.52   $131.50   $131.50  
  Purchase #4 $88.94   13.555%   $100.9958   $101.00   $101.00   $101.00  
  Purchase #5 $181.39   11.619%   $202.4657   $202.47   $202.45   $202.50  
  Purchase #6 $234.29   3.164%   $241.7029   $241.70   $241.70   $241.70  
  Purchase #7 $239.86   6.516%   $255.4893   $255.49   $255.50   $255.50  
  7 purchase totals = $1,339.46       $1,449.1265   $1,449.14   $1,449.10   $1,449.20