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 $60.53   4.871%   $63.4784   $63.48   $63.50   $63.50  
  Purchase #2 $68.43   4.837%   $71.74   $71.74   $71.75   $71.70  
  Purchase #3 $71.39   6.535%   $76.0553   $76.06   $76.05   $76.10  
  Purchase #4 $166.58   13.804%   $189.5747   $189.57   $189.55   $189.60  
  Purchase #5 $58.52   12.368%   $65.7578   $65.76   $65.75   $65.80  
  Purchase #6 $99.31   8.116%   $107.37   $107.37   $107.35   $107.40  
  Purchase #7 $233.60   4.457%   $244.0116   $244.01   $244.00   $244.00  
  7 purchase totals = $758.36       $817.9878   $817.99   $817.95   $818.10