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 $172.92   5.805%   $182.958   $182.96   $182.95   $183.00  
  Purchase #2 $152.65   13.554%   $173.3402   $173.34   $173.35   $173.30  
  Purchase #3 $148.53   12.445%   $167.0146   $167.01   $167.00   $167.00  
  Purchase #4 $246.69   7.646%   $265.5519   $265.55   $265.55   $265.60  
  Purchase #5 $227.79   9.123%   $248.5713   $248.57   $248.55   $248.60  
  Purchase #6 $188.41   12.466%   $211.8972   $211.90   $211.90   $211.90  
  Purchase #7 $226.53   7.465%   $243.4405   $243.44   $243.45   $243.40  
  7 purchase totals = $1,363.52       $1,492.7737   $1,492.77   $1,492.75   $1,492.80