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 $24.41   7.770%   $26.3067   $26.31   $26.30   $26.30  
  Purchase #2 $45.94   13.138%   $51.9756   $51.98   $52.00   $52.00  
  Purchase #3 $212.77   13.211%   $240.879   $240.88   $240.90   $240.90  
  Purchase #4 $65.76   4.402%   $68.6548   $68.65   $68.65   $68.70  
  Purchase #5 $167.26   6.148%   $177.5431   $177.54   $177.55   $177.50  
  Purchase #6 $223.60   10.494%   $247.0646   $247.06   $247.05   $247.10  
  Purchase #7 $137.90   11.818%   $154.197   $154.20   $154.20   $154.20  
  7 purchase totals = $877.64       $966.6208   $966.62   $966.65   $966.70