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 $245.40   7.455%   $263.6946   $263.69   $263.70   $263.70  
  Purchase #2 $169.32   12.833%   $191.0488   $191.05   $191.05   $191.00  
  Purchase #3 $23.80   4.360%   $24.8377   $24.84   $24.85   $24.80  
  Purchase #4 $100.93   9.542%   $110.5607   $110.56   $110.55   $110.60  
  Purchase #5 $105.85   12.499%   $119.0802   $119.08   $119.10   $119.10  
  Purchase #6 $29.92   8.869%   $32.5736   $32.57   $32.55   $32.60  
  Purchase #7 $178.33   7.844%   $192.3182   $192.32   $192.30   $192.30  
  7 purchase totals = $853.55       $934.1138   $934.11   $934.10   $934.10