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 $58.39   11.201%   $64.9303   $64.93   $64.95   $64.90  
  Purchase #2 $163.63   13.178%   $185.1932   $185.19   $185.20   $185.20  
  Purchase #3 $163.84   12.378%   $184.1201   $184.12   $184.10   $184.10  
  Purchase #4 $195.59   13.686%   $222.3584   $222.36   $222.35   $222.40  
  Purchase #5 $65.52   8.260%   $70.932   $70.93   $70.95   $70.90  
  Purchase #6 $120.82   7.293%   $129.6314   $129.63   $129.65   $129.60  
  Purchase #7 $150.79   7.473%   $162.0585   $162.06   $162.05   $162.10  
  7 purchase totals = $918.58       $1,019.2239   $1,019.22   $1,019.25   $1,019.20