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 $57.54   9.319%   $62.9022   $62.90   $62.90   $62.90  
  Purchase #2 $239.37   13.638%   $272.0153   $272.02   $272.00   $272.00  
  Purchase #3 $225.74   9.530%   $247.253   $247.25   $247.25   $247.30  
  Purchase #4 $88.69   6.623%   $94.5639   $94.56   $94.55   $94.60  
  Purchase #5 $24.45   3.366%   $25.273   $25.27   $25.25   $25.30  
  Purchase #6 $231.51   11.159%   $257.3442   $257.34   $257.35   $257.30  
  Purchase #7 $180.43   6.605%   $192.3474   $192.35   $192.35   $192.30  
  7 purchase totals = $1,047.73       $1,151.6990   $1,151.69   $1,151.65   $1,151.70