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 $81.40   11.858%   $91.0524   $91.05   $91.05   $91.10  
  Purchase #2 $222.56   5.668%   $235.1747   $235.17   $235.15   $235.20  
  Purchase #3 $227.43   8.801%   $247.4461   $247.45   $247.45   $247.40  
  Purchase #4 $66.35   4.125%   $69.0869   $69.09   $69.10   $69.10  
  Purchase #5 $199.73   12.622%   $224.9399   $224.94   $224.95   $224.90  
  Purchase #6 $59.82   9.796%   $65.68   $65.68   $65.70   $65.70  
  Purchase #7 $92.37   4.731%   $96.74   $96.74   $96.75   $96.70  
  7 purchase totals = $949.66       $1,030.1200   $1,030.12   $1,030.15   $1,030.10