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 $55.94   7.574%   $60.1769   $60.18   $60.20   $60.20  
  Purchase #2 $191.95   9.464%   $210.1161   $210.12   $210.10   $210.10  
  Purchase #3 $150.82   9.702%   $165.4526   $165.45   $165.45   $165.50  
  Purchase #4 $118.97   9.248%   $129.9723   $129.97   $129.95   $130.00  
  Purchase #5 $205.62   3.723%   $213.2752   $213.28   $213.30   $213.30  
  Purchase #6 $49.67   11.136%   $55.2013   $55.20   $55.20   $55.20  
  Purchase #7 $220.96   3.644%   $229.0118   $229.01   $229.00   $229.00  
  7 purchase totals = $993.93       $1,063.2062   $1,063.21   $1,063.20   $1,063.30