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 $106.41   3.672%   $110.3174   $110.32   $110.30   $110.30  
  Purchase #2 $35.86   13.795%   $40.8069   $40.81   $40.80   $40.80  
  Purchase #3 $173.87   6.583%   $185.3159   $185.32   $185.30   $185.30  
  Purchase #4 $205.68   8.525%   $223.2142   $223.21   $223.20   $223.20  
  Purchase #5 $224.91   3.375%   $232.5007   $232.50   $232.50   $232.50  
  Purchase #6 $6.61   10.501%   $7.3041   $7.30   $7.30   $7.30  
  Purchase #7 $27.62   13.465%   $31.339   $31.34   $31.35   $31.30  
  7 purchase totals = $780.96       $830.7982   $830.80   $830.75   $830.70