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 $125.40   13.740%   $142.63   $142.63   $142.65   $142.60  
  Purchase #2 $197.58   13.357%   $223.9708   $223.97   $223.95   $224.00  
  Purchase #3 $169.87   5.797%   $179.7174   $179.72   $179.70   $179.70  
  Purchase #4 $150.87   13.224%   $170.821   $170.82   $170.80   $170.80  
  Purchase #5 $232.58   13.263%   $263.4271   $263.43   $263.45   $263.40  
  Purchase #6 $215.70   5.121%   $226.746   $226.75   $226.75   $226.70  
  Purchase #7 $59.57   9.104%   $64.9933   $64.99   $65.00   $65.00  
  7 purchase totals = $1,151.57       $1,272.3056   $1,272.31   $1,272.30   $1,272.20