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 $219.25   11.132%   $243.6569   $243.66   $243.65   $243.70  
  Purchase #2 $63.53   3.236%   $65.5858   $65.59   $65.60   $65.60  
  Purchase #3 $148.90   3.199%   $153.6633   $153.66   $153.65   $153.70  
  Purchase #4 $19.32   3.195%   $19.9373   $19.94   $19.95   $19.90  
  Purchase #5 $102.47   10.386%   $113.1125   $113.11   $113.10   $113.10  
  Purchase #6 $20.60   8.380%   $22.3263   $22.33   $22.35   $22.30  
  Purchase #7 $184.35   6.735%   $196.766   $196.77   $196.75   $196.80  
  7 purchase totals = $758.42       $815.0481   $815.06   $815.05   $815.10