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 $246.36   12.668%   $277.5689   $277.57   $277.55   $277.60  
  Purchase #2 $127.47   7.804%   $137.4178   $137.42   $137.40   $137.40  
  Purchase #3 $88.67   8.841%   $96.5093   $96.51   $96.50   $96.50  
  Purchase #4 $222.41   5.817%   $235.3476   $235.35   $235.35   $235.30  
  Purchase #5 $173.50   3.502%   $179.576   $179.58   $179.60   $179.60  
  Purchase #6 $202.68   11.399%   $225.7835   $225.78   $225.80   $225.80  
  Purchase #7 $87.72   5.687%   $92.7086   $92.71   $92.70   $92.70  
  7 purchase totals = $1,148.81       $1,244.9117   $1,244.92   $1,244.90   $1,244.90