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 $198.32   3.407%   $205.0768   $205.08   $205.10   $205.10  
  Purchase #2 $26.74   9.234%   $29.2092   $29.21   $29.20   $29.20  
  Purchase #3 $150.39   12.872%   $169.7482   $169.75   $169.75   $169.70  
  Purchase #4 $80.95   4.655%   $84.7182   $84.72   $84.70   $84.70  
  Purchase #5 $137.59   4.219%   $143.3949   $143.39   $143.40   $143.40  
  Purchase #6 $210.65   11.201%   $234.2449   $234.24   $234.25   $234.20  
  Purchase #7 $144.26   9.695%   $158.246   $158.25   $158.25   $158.20  
  7 purchase totals = $948.90       $1,024.6382   $1,024.64   $1,024.65   $1,024.50