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 $187.73   7.421%   $201.6614   $201.66   $201.65   $201.70  
  Purchase #2 $82.53   13.372%   $93.5659   $93.57   $93.55   $93.60  
  Purchase #3 $35.47   6.817%   $37.888   $37.89   $37.90   $37.90  
  Purchase #4 $89.35   9.369%   $97.7212   $97.72   $97.70   $97.70  
  Purchase #5 $200.89   13.592%   $228.195   $228.20   $228.20   $228.20  
  Purchase #6 $174.75   8.212%   $189.1005   $189.10   $189.10   $189.10  
  Purchase #7 $247.79   4.861%   $259.8351   $259.84   $259.85   $259.80  
  7 purchase totals = $1,018.51       $1,107.9671   $1,107.98   $1,107.95   $1,108.00