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 $23.50   6.259%   $24.9709   $24.97   $24.95   $25.00  
  Purchase #2 $148.54   7.349%   $159.4562   $159.46   $159.45   $159.50  
  Purchase #3 $84.72   4.745%   $88.74   $88.74   $88.75   $88.70  
  Purchase #4 $212.75   12.200%   $238.7055   $238.71   $238.70   $238.70  
  Purchase #5 $6.25   4.525%   $6.5328   $6.53   $6.55   $6.50  
  Purchase #6 $192.34   5.358%   $202.6456   $202.65   $202.65   $202.60  
  Purchase #7 $38.65   5.774%   $40.8817   $40.88   $40.90   $40.90  
  7 purchase totals = $706.75       $761.9327   $761.94   $761.95   $761.90