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 $182.84   10.313%   $201.6963   $201.70   $201.70   $201.70  
  Purchase #2 $52.58   11.560%   $58.6582   $58.66   $58.65   $58.70  
  Purchase #3 $23.33   10.565%   $25.7948   $25.79   $25.80   $25.80  
  Purchase #4 $118.92   10.138%   $130.9761   $130.98   $131.00   $131.00  
  Purchase #5 $77.95   5.657%   $82.3596   $82.36   $82.35   $82.40  
  Purchase #6 $181.83   10.824%   $201.5113   $201.51   $201.50   $201.50  
  Purchase #7 $232.81   5.557%   $245.7473   $245.75   $245.75   $245.70  
  7 purchase totals = $870.26       $946.7436   $946.75   $946.75   $946.80