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 $233.85   8.820%   $254.4756   $254.48   $254.50   $254.50  
  Purchase #2 $43.52   6.696%   $46.4341   $46.43   $46.45   $46.40  
  Purchase #3 $206.48   13.582%   $234.5241   $234.52   $234.50   $234.50  
  Purchase #4 $19.68   8.613%   $21.375   $21.38   $21.40   $21.40  
  Purchase #5 $209.87   6.628%   $223.7802   $223.78   $223.80   $223.80  
  Purchase #6 $102.92   13.220%   $116.526   $116.53   $116.55   $116.50  
  Purchase #7 $220.51   8.437%   $239.1144   $239.11   $239.10   $239.10  
  7 purchase totals = $1,036.83       $1,136.2294   $1,136.23   $1,136.30   $1,136.20