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 $44.74   4.654%   $46.8222   $46.82   $46.80   $46.80  
  Purchase #2 $207.82   7.305%   $223.0013   $223.00   $223.00   $223.00  
  Purchase #3 $182.57   13.445%   $207.1165   $207.12   $207.10   $207.10  
  Purchase #4 $46.67   11.304%   $51.9456   $51.95   $51.95   $51.90  
  Purchase #5 $218.45   3.228%   $225.5016   $225.50   $225.50   $225.50  
  Purchase #6 $244.97   13.760%   $278.6779   $278.68   $278.70   $278.70  
  Purchase #7 $192.90   4.441%   $201.4667   $201.47   $201.45   $201.50  
  7 purchase totals = $1,138.12       $1,234.5318   $1,234.54   $1,234.50   $1,234.50