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 $57.91   7.834%   $62.4467   $62.45   $62.45   $62.40  
  Purchase #2 $235.49   8.529%   $255.5749   $255.57   $255.55   $255.60  
  Purchase #3 $208.48   3.629%   $216.0457   $216.05   $216.05   $216.00  
  Purchase #4 $148.45   7.375%   $159.3982   $159.40   $159.40   $159.40  
  Purchase #5 $126.73   7.112%   $135.743   $135.74   $135.75   $135.70  
  Purchase #6 $60.62   11.200%   $67.4094   $67.41   $67.40   $67.40  
  Purchase #7 $33.85   12.362%   $38.0345   $38.03   $38.05   $38.00  
  7 purchase totals = $871.53       $934.6524   $934.65   $934.65   $934.50