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 $194.64   12.638%   $219.2386   $219.24   $219.25   $219.20  
  Purchase #2 $241.50   7.806%   $260.3515   $260.35   $260.35   $260.40  
  Purchase #3 $182.29   12.665%   $205.377   $205.38   $205.40   $205.40  
  Purchase #4 $224.36   8.432%   $243.278   $243.28   $243.30   $243.30  
  Purchase #5 $61.51   6.211%   $65.3304   $65.33   $65.35   $65.30  
  Purchase #6 $110.84   9.561%   $121.4374   $121.44   $121.45   $121.40  
  Purchase #7 $237.82   4.330%   $248.1176   $248.12   $248.10   $248.10  
  7 purchase totals = $1,252.96       $1,363.1305   $1,363.14   $1,363.20   $1,363.10