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 $203.77   3.684%   $211.2769   $211.28   $211.30   $211.30  
  Purchase #2 $58.65   11.431%   $65.3543   $65.35   $65.35   $65.40  
  Purchase #3 $105.65   13.648%   $120.0691   $120.07   $120.05   $120.10  
  Purchase #4 $88.83   4.618%   $92.9322   $92.93   $92.95   $92.90  
  Purchase #5 $127.52   12.229%   $143.1144   $143.11   $143.10   $143.10  
  Purchase #6 $219.79   9.564%   $240.8107   $240.81   $240.80   $240.80  
  Purchase #7 $92.47   4.824%   $96.9308   $96.93   $96.95   $96.90  
  7 purchase totals = $896.68       $970.4884   $970.48   $970.50   $970.50