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 $47.82   12.128%   $53.6196   $53.62   $53.60   $53.60  
  Purchase #2 $234.78   7.280%   $251.872   $251.87   $251.85   $251.90  
  Purchase #3 $153.79   7.467%   $165.2735   $165.27   $165.25   $165.30  
  Purchase #4 $234.72   13.426%   $266.2335   $266.23   $266.25   $266.20  
  Purchase #5 $70.26   5.841%   $74.3639   $74.36   $74.35   $74.40  
  Purchase #6 $187.79   3.404%   $194.1824   $194.18   $194.20   $194.20  
  Purchase #7 $105.45   13.532%   $119.7195   $119.72   $119.70   $119.70  
  7 purchase totals = $1,034.61       $1,125.2644   $1,125.25   $1,125.20   $1,125.30