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 $216.26   10.192%   $238.3012   $238.30   $238.30   $238.30  
  Purchase #2 $13.32   8.697%   $14.4784   $14.48   $14.50   $14.50  
  Purchase #3 $160.86   5.433%   $169.5995   $169.60   $169.60   $169.60  
  Purchase #4 $77.38   13.190%   $87.5864   $87.59   $87.60   $87.60  
  Purchase #5 $208.35   10.779%   $230.808   $230.81   $230.80   $230.80  
  Purchase #6 $64.69   9.483%   $70.8246   $70.82   $70.80   $70.80  
  Purchase #7 $123.63   8.807%   $134.5181   $134.52   $134.50   $134.50  
  7 purchase totals = $864.49       $946.1162   $946.12   $946.10   $946.10