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 $214.87   12.767%   $242.3025   $242.30   $242.30   $242.30  
  Purchase #2 $45.50   5.245%   $47.8865   $47.89   $47.90   $47.90  
  Purchase #3 $231.33   6.627%   $246.6602   $246.66   $246.65   $246.70  
  Purchase #4 $147.92   9.161%   $161.471   $161.47   $161.45   $161.50  
  Purchase #5 $218.82   6.274%   $232.5488   $232.55   $232.55   $232.50  
  Purchase #6 $90.93   13.253%   $102.981   $102.98   $103.00   $103.00  
  Purchase #7 $25.36   10.363%   $27.9881   $27.99   $28.00   $28.00  
  7 purchase totals = $974.73       $1,061.8381   $1,061.84   $1,061.85   $1,061.90