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 $95.39   11.658%   $106.5106   $106.51   $106.50   $106.50  
  Purchase #2 $39.87   10.458%   $44.0396   $44.04   $44.05   $44.00  
  Purchase #3 $201.29   10.349%   $222.1215   $222.12   $222.10   $222.10  
  Purchase #4 $225.73   12.837%   $254.707   $254.71   $254.70   $254.70  
  Purchase #5 $100.71   9.513%   $110.2905   $110.29   $110.30   $110.30  
  Purchase #6 $99.87   4.840%   $104.7037   $104.70   $104.70   $104.70  
  Purchase #7 $222.73   12.701%   $251.0189   $251.02   $251.00   $251.00  
  7 purchase totals = $985.59       $1,093.3918   $1,093.39   $1,093.35   $1,093.30