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 $211.41   9.868%   $232.2719   $232.27   $232.25   $232.30  
  Purchase #2 $175.30   6.367%   $186.4614   $186.46   $186.45   $186.50  
  Purchase #3 $212.63   7.296%   $228.1435   $228.14   $228.15   $228.10  
  Purchase #4 $99.45   3.581%   $103.0113   $103.01   $103.00   $103.00  
  Purchase #5 $115.67   3.840%   $120.1117   $120.11   $120.10   $120.10  
  Purchase #6 $93.57   11.130%   $103.9843   $103.98   $104.00   $104.00  
  Purchase #7 $37.84   6.504%   $40.3011   $40.30   $40.30   $40.30  
  7 purchase totals = $945.87       $1,014.2852   $1,014.27   $1,014.25   $1,014.30