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 $67.74   8.211%   $73.3021   $73.30   $73.30   $73.30  
  Purchase #2 $59.45   7.452%   $63.8802   $63.88   $63.90   $63.90  
  Purchase #3 $130.32   8.460%   $141.3451   $141.35   $141.35   $141.30  
  Purchase #4 $211.96   5.422%   $223.4525   $223.45   $223.45   $223.50  
  Purchase #5 $203.58   5.166%   $214.0969   $214.10   $214.10   $214.10  
  Purchase #6 $76.44   5.316%   $80.5036   $80.50   $80.50   $80.50  
  Purchase #7 $50.43   9.124%   $55.0312   $55.03   $55.05   $55.00  
  7 purchase totals = $799.92       $851.6116   $851.61   $851.65   $851.60