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 $69.38   7.111%   $74.3136   $74.31   $74.30   $74.30  
  Purchase #2 $224.55   12.517%   $252.6569   $252.66   $252.65   $252.70  
  Purchase #3 $143.85   11.142%   $159.8778   $159.88   $159.90   $159.90  
  Purchase #4 $183.60   5.431%   $193.5713   $193.57   $193.55   $193.60  
  Purchase #5 $47.77   3.754%   $49.5633   $49.56   $49.55   $49.60  
  Purchase #6 $62.76   3.334%   $64.8524   $64.85   $64.85   $64.90  
  Purchase #7 $226.36   3.803%   $234.9685   $234.97   $234.95   $235.00  
  7 purchase totals = $958.27       $1,029.8038   $1,029.80   $1,029.75   $1,030.00