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 $232.72   13.831%   $264.9075   $264.91   $264.90   $264.90  
  Purchase #2 $195.29   5.594%   $206.2145   $206.21   $206.20   $206.20  
  Purchase #3 $38.83   5.376%   $40.9175   $40.92   $40.90   $40.90  
  Purchase #4 $46.86   13.447%   $53.1613   $53.16   $53.15   $53.20  
  Purchase #5 $156.93   11.170%   $174.4591   $174.46   $174.45   $174.50  
  Purchase #6 $219.58   3.468%   $227.195   $227.20   $227.20   $227.20  
  Purchase #7 $60.77   11.544%   $67.7853   $67.79   $67.80   $67.80  
  7 purchase totals = $950.98       $1,034.6402   $1,034.65   $1,034.60   $1,034.70