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 $197.49   8.371%   $214.0219   $214.02   $214.00   $214.00  
  Purchase #2 $36.54   8.534%   $39.6583   $39.66   $39.65   $39.70  
  Purchase #3 $110.43   6.690%   $117.8178   $117.82   $117.80   $117.80  
  Purchase #4 $172.40   9.231%   $188.3142   $188.31   $188.30   $188.30  
  Purchase #5 $97.45   9.450%   $106.659   $106.66   $106.65   $106.70  
  Purchase #6 $199.57   5.157%   $209.8618   $209.86   $209.85   $209.90  
  Purchase #7 $202.54   13.534%   $229.9518   $229.95   $229.95   $230.00  
  7 purchase totals = $1,016.42       $1,106.2848   $1,106.28   $1,106.20   $1,106.40