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 $246.28   8.112%   $266.2582   $266.26   $266.25   $266.30  
  Purchase #2 $45.36   3.283%   $46.8492   $46.85   $46.85   $46.80  
  Purchase #3 $199.64   6.442%   $212.5008   $212.50   $212.50   $212.50  
  Purchase #4 $160.94   10.171%   $177.3092   $177.31   $177.30   $177.30  
  Purchase #5 $225.41   7.153%   $241.5336   $241.53   $241.55   $241.50  
  Purchase #6 $213.26   4.507%   $222.8716   $222.87   $222.85   $222.90  
  Purchase #7 $37.81   6.152%   $40.1361   $40.14   $40.15   $40.10  
  7 purchase totals = $1,128.70       $1,207.4587   $1,207.46   $1,207.45   $1,207.40