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 $191.33   13.270%   $216.7195   $216.72   $216.70   $216.70  
  Purchase #2 $244.63   7.592%   $263.2023   $263.20   $263.20   $263.20  
  Purchase #3 $247.60   7.585%   $266.3805   $266.38   $266.40   $266.40  
  Purchase #4 $112.45   3.459%   $116.3396   $116.34   $116.35   $116.30  
  Purchase #5 $99.74   10.590%   $110.3025   $110.30   $110.30   $110.30  
  Purchase #6 $26.54   5.204%   $27.9211   $27.92   $27.90   $27.90  
  Purchase #7 $10.69   4.247%   $11.144   $11.14   $11.15   $11.10  
  7 purchase totals = $932.98       $1,012.0095   $1,012.00   $1,012.00   $1,011.90