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 $88.92   9.810%   $97.6431   $97.64   $97.65   $97.60  
  Purchase #2 $209.26   6.739%   $223.362   $223.36   $223.35   $223.40  
  Purchase #3 $195.65   10.873%   $216.923   $216.92   $216.90   $216.90  
  Purchase #4 $54.39   9.270%   $59.432   $59.43   $59.45   $59.40  
  Purchase #5 $228.93   4.623%   $239.5134   $239.51   $239.50   $239.50  
  Purchase #6 $43.26   6.664%   $46.1428   $46.14   $46.15   $46.10  
  Purchase #7 $145.50   3.807%   $151.0392   $151.04   $151.05   $151.00  
  7 purchase totals = $965.91       $1,034.0555   $1,034.04   $1,034.05   $1,033.90