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 $177.89   9.411%   $194.6312   $194.63   $194.65   $194.60  
  Purchase #2 $167.26   10.454%   $184.7454   $184.75   $184.75   $184.70  
  Purchase #3 $50.51   4.120%   $52.591   $52.59   $52.60   $52.60  
  Purchase #4 $66.91   13.412%   $75.884   $75.88   $75.90   $75.90  
  Purchase #5 $88.69   9.323%   $96.9586   $96.96   $96.95   $97.00  
  Purchase #6 $140.86   8.461%   $152.7782   $152.78   $152.80   $152.80  
  Purchase #7 $238.64   9.643%   $261.6521   $261.65   $261.65   $261.70  
  7 purchase totals = $930.76       $1,019.2405   $1,019.24   $1,019.30   $1,019.30