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 $58.38   3.686%   $60.5319   $60.53   $60.55   $60.50  
  Purchase #2 $190.64   13.218%   $215.8388   $215.84   $215.85   $215.80  
  Purchase #3 $207.96   7.334%   $223.2118   $223.21   $223.20   $223.20  
  Purchase #4 $141.41   10.216%   $155.8564   $155.86   $155.85   $155.90  
  Purchase #5 $197.87   9.337%   $216.3451   $216.35   $216.35   $216.30  
  Purchase #6 $149.61   10.575%   $165.4313   $165.43   $165.45   $165.40  
  Purchase #7 $185.29   6.648%   $197.6081   $197.61   $197.60   $197.60  
  7 purchase totals = $1,131.16       $1,234.8234   $1,234.83   $1,234.85   $1,234.70