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 $113.81   11.831%   $127.2749   $127.27   $127.25   $127.30  
  Purchase #2 $219.27   8.122%   $237.0791   $237.08   $237.10   $237.10  
  Purchase #3 $70.27   5.745%   $74.307   $74.31   $74.30   $74.30  
  Purchase #4 $26.98   8.648%   $29.3132   $29.31   $29.30   $29.30  
  Purchase #5 $213.50   4.622%   $223.368   $223.37   $223.35   $223.40  
  Purchase #6 $210.29   3.594%   $217.8478   $217.85   $217.85   $217.80  
  Purchase #7 $110.35   13.627%   $125.3874   $125.39   $125.40   $125.40  
  7 purchase totals = $964.47       $1,034.5774   $1,034.58   $1,034.55   $1,034.60