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 $93.28   9.382%   $102.0315   $102.03   $102.05   $102.00  
  Purchase #2 $226.56   6.610%   $241.5356   $241.54   $241.55   $241.50  
  Purchase #3 $226.72   8.589%   $246.193   $246.19   $246.20   $246.20  
  Purchase #4 $132.93   12.851%   $150.0128   $150.01   $150.00   $150.00  
  Purchase #5 $188.36   4.782%   $197.3674   $197.37   $197.35   $197.40  
  Purchase #6 $112.59   4.334%   $117.4697   $117.47   $117.45   $117.50  
  Purchase #7 $43.27   11.381%   $48.1946   $48.19   $48.20   $48.20  
  7 purchase totals = $1,023.71       $1,102.8046   $1,102.80   $1,102.80   $1,102.80