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 $54.92   6.611%   $58.5508   $58.55   $58.55   $58.60  
  Purchase #2 $218.97   9.865%   $240.5714   $240.57   $240.55   $240.60  
  Purchase #3 $135.71   5.601%   $143.3111   $143.31   $143.30   $143.30  
  Purchase #4 $240.58   9.655%   $263.808   $263.81   $263.80   $263.80  
  Purchase #5 $110.75   12.842%   $124.9725   $124.97   $124.95   $125.00  
  Purchase #6 $11.83   11.559%   $13.1974   $13.20   $13.20   $13.20  
  Purchase #7 $235.80   9.299%   $257.727   $257.73   $257.75   $257.70  
  7 purchase totals = $1,008.56       $1,102.1382   $1,102.14   $1,102.10   $1,102.20