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 $236.98   13.224%   $268.3182   $268.32   $268.30   $268.30  
  Purchase #2 $138.37   4.530%   $144.6382   $144.64   $144.65   $144.60  
  Purchase #3 $48.46   4.273%   $50.5307   $50.53   $50.55   $50.50  
  Purchase #4 $130.67   7.337%   $140.2573   $140.26   $140.25   $140.30  
  Purchase #5 $224.53   7.317%   $240.9589   $240.96   $240.95   $241.00  
  Purchase #6 $223.94   8.685%   $243.3892   $243.39   $243.40   $243.40  
  Purchase #7 $113.26   4.313%   $118.1449   $118.14   $118.15   $118.10  
  7 purchase totals = $1,116.21       $1,206.2374   $1,206.24   $1,206.25   $1,206.20