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 $193.77   11.578%   $216.2047   $216.20   $216.20   $216.20  
  Purchase #2 $50.85   10.628%   $56.2543   $56.25   $56.25   $56.30  
  Purchase #3 $187.45   9.607%   $205.4583   $205.46   $205.45   $205.50  
  Purchase #4 $66.95   4.362%   $69.8704   $69.87   $69.85   $69.90  
  Purchase #5 $57.62   10.347%   $63.5819   $63.58   $63.60   $63.60  
  Purchase #6 $110.52   10.515%   $122.1412   $122.14   $122.15   $122.10  
  Purchase #7 $236.26   13.370%   $267.848   $267.85   $267.85   $267.80  
  7 purchase totals = $903.42       $1,001.3588   $1,001.35   $1,001.35   $1,001.40