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 $121.71   3.702%   $126.2157   $126.22   $126.20   $126.20  
  Purchase #2 $221.74   6.816%   $236.8538   $236.85   $236.85   $236.90  
  Purchase #3 $128.72   5.718%   $136.0802   $136.08   $136.10   $136.10  
  Purchase #4 $217.44   5.611%   $229.6406   $229.64   $229.65   $229.60  
  Purchase #5 $56.92   7.392%   $61.1275   $61.13   $61.15   $61.10  
  Purchase #6 $232.48   8.146%   $251.4178   $251.42   $251.40   $251.40  
  Purchase #7 $137.87   11.227%   $153.3487   $153.35   $153.35   $153.30  
  7 purchase totals = $1,116.88       $1,194.6843   $1,194.69   $1,194.70   $1,194.60