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 $86.89   12.759%   $97.9763   $97.98   $98.00   $98.00  
  Purchase #2 $244.73   3.637%   $253.6308   $253.63   $253.65   $253.60  
  Purchase #3 $54.39   6.766%   $58.07   $58.07   $58.05   $58.10  
  Purchase #4 $163.38   10.398%   $180.3683   $180.37   $180.35   $180.40  
  Purchase #5 $225.43   7.129%   $241.5009   $241.50   $241.50   $241.50  
  Purchase #6 $128.46   10.147%   $141.4948   $141.49   $141.50   $141.50  
  Purchase #7 $39.29   13.308%   $44.5187   $44.52   $44.50   $44.50  
  7 purchase totals = $942.57       $1,017.5598   $1,017.56   $1,017.55   $1,017.60