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 $75.62   10.648%   $83.672   $83.67   $83.65   $83.70  
  Purchase #2 $23.89   4.851%   $25.0489   $25.05   $25.05   $25.00  
  Purchase #3 $114.68   12.408%   $128.9095   $128.91   $128.90   $128.90  
  Purchase #4 $41.26   8.272%   $44.673   $44.67   $44.65   $44.70  
  Purchase #5 $93.31   6.554%   $99.4255   $99.43   $99.45   $99.40  
  Purchase #6 $229.34   13.343%   $259.9408   $259.94   $259.95   $259.90  
  Purchase #7 $51.75   4.148%   $53.8966   $53.90   $53.90   $53.90  
  7 purchase totals = $629.85       $695.5663   $695.57   $695.55   $695.50