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 $91.52   7.364%   $98.2595   $98.26   $98.25   $98.30  
  Purchase #2 $176.81   9.364%   $193.3665   $193.37   $193.35   $193.40  
  Purchase #3 $31.33   3.611%   $32.4613   $32.46   $32.45   $32.50  
  Purchase #4 $247.46   13.369%   $280.5429   $280.54   $280.55   $280.50  
  Purchase #5 $58.67   11.220%   $65.2528   $65.25   $65.25   $65.30  
  Purchase #6 $196.47   6.838%   $209.9046   $209.90   $209.90   $209.90  
  Purchase #7 $109.84   4.717%   $115.0212   $115.02   $115.00   $115.00  
  7 purchase totals = $912.10       $994.8088   $994.80   $994.75   $994.90