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 $211.78   11.812%   $236.7955   $236.80   $236.80   $236.80  
  Purchase #2 $201.97   8.597%   $219.3334   $219.33   $219.35   $219.30  
  Purchase #3 $159.41   5.623%   $168.3736   $168.37   $168.35   $168.40  
  Purchase #4 $169.72   13.193%   $192.1112   $192.11   $192.10   $192.10  
  Purchase #5 $206.33   10.754%   $228.5187   $228.52   $228.50   $228.50  
  Purchase #6 $85.38   10.374%   $94.2373   $94.24   $94.25   $94.20  
  Purchase #7 $211.65   5.146%   $222.5415   $222.54   $222.55   $222.50  
  7 purchase totals = $1,246.24       $1,361.9112   $1,361.91   $1,361.90   $1,361.80