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 $169.65   11.769%   $189.6161   $189.62   $189.60   $189.60  
  Purchase #2 $62.98   3.128%   $64.95   $64.95   $64.95   $65.00  
  Purchase #3 $88.86   6.114%   $94.2929   $94.29   $94.30   $94.30  
  Purchase #4 $110.49   10.449%   $122.0351   $122.04   $122.05   $122.00  
  Purchase #5 $229.66   4.290%   $239.5124   $239.51   $239.50   $239.50  
  Purchase #6 $227.50   10.685%   $251.8084   $251.81   $251.80   $251.80  
  Purchase #7 $228.29   8.636%   $248.0051   $248.01   $248.00   $248.00  
  7 purchase totals = $1,117.43       $1,210.2200   $1,210.23   $1,210.20   $1,210.20