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 $213.56   4.784%   $223.7767   $223.78   $223.80   $223.80  
  Purchase #2 $136.79   11.376%   $152.3512   $152.35   $152.35   $152.40  
  Purchase #3 $57.58   13.295%   $65.2353   $65.24   $65.25   $65.20  
  Purchase #4 $93.31   12.256%   $104.7461   $104.75   $104.75   $104.70  
  Purchase #5 $24.30   12.147%   $27.2517   $27.25   $27.25   $27.30  
  Purchase #6 $244.39   3.475%   $252.8826   $252.88   $252.90   $252.90  
  Purchase #7 $204.77   11.797%   $228.9267   $228.93   $228.95   $228.90  
  7 purchase totals = $974.70       $1,055.1703   $1,055.18   $1,055.25   $1,055.20