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 $106.91   10.431%   $118.0618   $118.06   $118.05   $118.10  
  Purchase #2 $201.28   12.141%   $225.7174   $225.72   $225.70   $225.70  
  Purchase #3 $204.66   3.604%   $212.0359   $212.04   $212.05   $212.00  
  Purchase #4 $25.87   4.371%   $27.0008   $27.00   $27.00   $27.00  
  Purchase #5 $87.64   11.325%   $97.5652   $97.57   $97.55   $97.60  
  Purchase #6 $248.47   12.489%   $279.5014   $279.50   $279.50   $279.50  
  Purchase #7 $32.56   8.385%   $35.2902   $35.29   $35.30   $35.30  
  7 purchase totals = $907.39       $995.1727   $995.18   $995.15   $995.20