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 $82.37   13.132%   $93.1868   $93.19   $93.20   $93.20  
  Purchase #2 $216.81   11.298%   $241.3052   $241.31   $241.30   $241.30  
  Purchase #3 $219.62   9.121%   $239.6515   $239.65   $239.65   $239.70  
  Purchase #4 $238.30   9.348%   $260.5763   $260.58   $260.60   $260.60  
  Purchase #5 $116.86   11.160%   $129.9016   $129.90   $129.90   $129.90  
  Purchase #6 $124.70   6.551%   $132.8691   $132.87   $132.85   $132.90  
  Purchase #7 $74.64   13.313%   $84.5768   $84.58   $84.60   $84.60  
  7 purchase totals = $1,073.30       $1,182.0673   $1,182.08   $1,182.10   $1,182.20