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 $91.51   6.576%   $97.5277   $97.53   $97.55   $97.50  
  Purchase #2 $171.98   6.412%   $183.0074   $183.01   $183.00   $183.00  
  Purchase #3 $155.45   5.361%   $163.7837   $163.78   $163.80   $163.80  
  Purchase #4 $162.26   5.359%   $170.9555   $170.96   $170.95   $171.00  
  Purchase #5 $200.36   11.446%   $223.2932   $223.29   $223.30   $223.30  
  Purchase #6 $64.87   12.356%   $72.8853   $72.89   $72.90   $72.90  
  Purchase #7 $147.54   8.273%   $159.746   $159.75   $159.75   $159.70  
  7 purchase totals = $993.97       $1,071.1988   $1,071.21   $1,071.25   $1,071.20