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 $95.64   10.815%   $105.9835   $105.98   $106.00   $106.00  
  Purchase #2 $179.31   6.761%   $191.4331   $191.43   $191.45   $191.40  
  Purchase #3 $240.97   9.400%   $263.6212   $263.62   $263.60   $263.60  
  Purchase #4 $83.92   13.404%   $95.1686   $95.17   $95.15   $95.20  
  Purchase #5 $60.50   12.338%   $67.9645   $67.96   $67.95   $68.00  
  Purchase #6 $6.86   12.361%   $7.708   $7.71   $7.70   $7.70  
  Purchase #7 $177.26   7.470%   $190.5013   $190.50   $190.50   $190.50  
  7 purchase totals = $844.46       $922.3802   $922.37   $922.35   $922.40