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 $94.58   7.815%   $101.9714   $101.97   $101.95   $102.00  
  Purchase #2 $20.41   10.142%   $22.48   $22.48   $22.50   $22.50  
  Purchase #3 $17.44   10.742%   $19.3134   $19.31   $19.30   $19.30  
  Purchase #4 $62.50   7.219%   $67.0119   $67.01   $67.00   $67.00  
  Purchase #5 $34.25   6.509%   $36.4793   $36.48   $36.50   $36.50  
  Purchase #6 $32.72   6.860%   $34.9646   $34.96   $34.95   $35.00  
  Purchase #7 $141.51   4.257%   $147.5341   $147.53   $147.55   $147.50  
  7 purchase totals = $403.41       $429.7547   $429.74   $429.75   $429.80