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 $54.96   9.440%   $60.1482   $60.15   $60.15   $60.10  
  Purchase #2 $78.46   11.873%   $87.7756   $87.78   $87.80   $87.80  
  Purchase #3 $35.36   3.608%   $36.6358   $36.64   $36.65   $36.60  
  Purchase #4 $219.53   6.735%   $234.3153   $234.32   $234.30   $234.30  
  Purchase #5 $94.80   12.606%   $106.7505   $106.75   $106.75   $106.80  
  Purchase #6 $185.79   13.594%   $211.0463   $211.05   $211.05   $211.00  
  Purchase #7 $246.37   12.244%   $276.5355   $276.54   $276.55   $276.50  
  7 purchase totals = $915.27       $1,013.2072   $1,013.23   $1,013.25   $1,013.10