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 $89.51   5.240%   $94.2003   $94.20   $94.20   $94.20  
  Purchase #2 $134.52   8.570%   $146.0484   $146.05   $146.05   $146.00  
  Purchase #3 $153.86   6.190%   $163.3839   $163.38   $163.40   $163.40  
  Purchase #4 $101.28   9.156%   $110.5532   $110.55   $110.55   $110.60  
  Purchase #5 $85.93   12.859%   $96.9797   $96.98   $97.00   $97.00  
  Purchase #6 $201.27   8.405%   $218.1867   $218.19   $218.20   $218.20  
  Purchase #7 $238.38   13.646%   $270.9093   $270.91   $270.90   $270.90  
  7 purchase totals = $1,004.75       $1,100.2615   $1,100.26   $1,100.30   $1,100.30