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 $125.57   7.772%   $135.3293   $135.33   $135.35   $135.30  
  Purchase #2 $185.40   9.140%   $202.3456   $202.35   $202.35   $202.30  
  Purchase #3 $216.52   11.673%   $241.7944   $241.79   $241.80   $241.80  
  Purchase #4 $194.68   8.735%   $211.6853   $211.69   $211.70   $211.70  
  Purchase #5 $87.93   9.476%   $96.2622   $96.26   $96.25   $96.30  
  Purchase #6 $57.71   6.823%   $61.6476   $61.65   $61.65   $61.60  
  Purchase #7 $68.38   6.659%   $72.9334   $72.93   $72.95   $72.90  
  7 purchase totals = $936.19       $1,021.9978   $1,022.00   $1,022.05   $1,021.90