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 $59.51   3.378%   $61.5202   $61.52   $61.50   $61.50  
  Purchase #2 $240.44   6.802%   $256.7947   $256.79   $256.80   $256.80  
  Purchase #3 $95.42   13.560%   $108.359   $108.36   $108.35   $108.40  
  Purchase #4 $157.70   9.794%   $173.1451   $173.15   $173.15   $173.10  
  Purchase #5 $134.78   11.560%   $150.3606   $150.36   $150.35   $150.40  
  Purchase #6 $41.94   12.645%   $47.2433   $47.24   $47.25   $47.20  
  Purchase #7 $201.36   6.214%   $213.8725   $213.87   $213.85   $213.90  
  7 purchase totals = $931.15       $1,011.2954   $1,011.29   $1,011.25   $1,011.30