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 $65.97   9.457%   $72.2088   $72.21   $72.20   $72.20  
  Purchase #2 $201.58   4.729%   $211.1127   $211.11   $211.10   $211.10  
  Purchase #3 $205.77   9.822%   $225.9807   $225.98   $226.00   $226.00  
  Purchase #4 $60.66   11.652%   $67.7281   $67.73   $67.75   $67.70  
  Purchase #5 $196.37   5.518%   $207.2057   $207.21   $207.20   $207.20  
  Purchase #6 $191.25   6.576%   $203.8266   $203.83   $203.85   $203.80  
  Purchase #7 $48.64   3.159%   $50.1765   $50.18   $50.20   $50.20  
  7 purchase totals = $970.24       $1,038.2391   $1,038.25   $1,038.30   $1,038.20