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 $239.26   6.274%   $254.2712   $254.27   $254.25   $254.30  
  Purchase #2 $58.27   13.166%   $65.9418   $65.94   $65.95   $65.90  
  Purchase #3 $191.95   4.222%   $200.0541   $200.05   $200.05   $200.10  
  Purchase #4 $77.65   13.506%   $88.1374   $88.14   $88.15   $88.10  
  Purchase #5 $106.52   6.372%   $113.3075   $113.31   $113.30   $113.30  
  Purchase #6 $182.79   6.177%   $194.0809   $194.08   $194.10   $194.10  
  Purchase #7 $110.70   13.796%   $125.9722   $125.97   $125.95   $126.00  
  7 purchase totals = $967.14       $1,041.7651   $1,041.76   $1,041.75   $1,041.80