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 $85.52   12.550%   $96.2528   $96.25   $96.25   $96.30  
  Purchase #2 $126.91   11.121%   $141.0237   $141.02   $141.00   $141.00  
  Purchase #3 $75.66   9.438%   $82.8008   $82.80   $82.80   $82.80  
  Purchase #4 $8.79   11.208%   $9.7752   $9.78   $9.80   $9.80  
  Purchase #5 $118.55   11.742%   $132.4701   $132.47   $132.45   $132.50  
  Purchase #6 $86.30   12.441%   $97.0366   $97.04   $97.05   $97.00  
  Purchase #7 $81.71   12.443%   $91.8772   $91.88   $91.90   $91.90  
  7 purchase totals = $583.44       $651.2364   $651.24   $651.25   $651.30