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 $201.39   10.736%   $223.0112   $223.01   $223.00   $223.00  
  Purchase #2 $14.97   13.205%   $16.9468   $16.95   $16.95   $16.90  
  Purchase #3 $75.88   7.814%   $81.8093   $81.81   $81.80   $81.80  
  Purchase #4 $72.67   12.428%   $81.7014   $81.70   $81.70   $81.70  
  Purchase #5 $235.43   11.639%   $262.8317   $262.83   $262.85   $262.80  
  Purchase #6 $23.37   10.848%   $25.9052   $25.91   $25.90   $25.90  
  Purchase #7 $63.55   3.459%   $65.7482   $65.75   $65.75   $65.70  
  7 purchase totals = $687.26       $757.9538   $757.96   $757.95   $757.80