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 $168.33   13.653%   $191.3121   $191.31   $191.30   $191.30  
  Purchase #2 $196.32   8.152%   $212.324   $212.32   $212.30   $212.30  
  Purchase #3 $17.51   11.205%   $19.472   $19.47   $19.45   $19.50  
  Purchase #4 $87.94   9.378%   $96.187   $96.19   $96.20   $96.20  
  Purchase #5 $69.86   9.539%   $76.5239   $76.52   $76.50   $76.50  
  Purchase #6 $117.60   5.804%   $124.4255   $124.43   $124.45   $124.40  
  Purchase #7 $141.80   6.177%   $150.559   $150.56   $150.55   $150.60  
  7 purchase totals = $799.36       $870.8035   $870.80   $870.75   $870.80