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 $96.26   8.140%   $104.0956   $104.10   $104.10   $104.10  
  Purchase #2 $211.93   5.391%   $223.3551   $223.36   $223.35   $223.40  
  Purchase #3 $24.39   6.119%   $25.8824   $25.88   $25.90   $25.90  
  Purchase #4 $125.76   9.795%   $138.0782   $138.08   $138.10   $138.10  
  Purchase #5 $171.79   12.516%   $193.2912   $193.29   $193.30   $193.30  
  Purchase #6 $212.60   10.196%   $234.2767   $234.28   $234.30   $234.30  
  Purchase #7 $32.77   8.495%   $35.5538   $35.55   $35.55   $35.60  
  7 purchase totals = $875.50       $954.5330   $954.54   $954.60   $954.70