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 $208.58   8.810%   $226.9559   $226.96   $226.95   $227.00  
  Purchase #2 $21.93   7.556%   $23.587   $23.59   $23.60   $23.60  
  Purchase #3 $141.35   13.777%   $160.8238   $160.82   $160.80   $160.80  
  Purchase #4 $121.52   5.681%   $128.4236   $128.42   $128.40   $128.40  
  Purchase #5 $101.27   6.535%   $107.888   $107.89   $107.90   $107.90  
  Purchase #6 $201.39   10.334%   $222.2016   $222.20   $222.20   $222.20  
  Purchase #7 $192.55   5.777%   $203.6736   $203.67   $203.65   $203.70  
  7 purchase totals = $988.59       $1,073.5535   $1,073.55   $1,073.50   $1,073.60