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 $217.63   11.742%   $243.1841   $243.18   $243.20   $243.20  
  Purchase #2 $50.73   4.853%   $53.1919   $53.19   $53.20   $53.20  
  Purchase #3 $150.52   10.157%   $165.8083   $165.81   $165.80   $165.80  
  Purchase #4 $233.99   8.575%   $254.0546   $254.05   $254.05   $254.10  
  Purchase #5 $145.29   3.160%   $149.8812   $149.88   $149.90   $149.90  
  Purchase #6 $81.34   8.762%   $88.467   $88.47   $88.45   $88.50  
  Purchase #7 $93.66   12.489%   $105.3572   $105.36   $105.35   $105.40  
  7 purchase totals = $973.16       $1,059.9443   $1,059.94   $1,059.95   $1,060.10