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 $237.48   11.605%   $265.0396   $265.04   $265.05   $265.00  
  Purchase #2 $245.25   3.712%   $254.3537   $254.35   $254.35   $254.40  
  Purchase #3 $100.31   13.251%   $113.6021   $113.60   $113.60   $113.60  
  Purchase #4 $150.69   11.290%   $167.7029   $167.70   $167.70   $167.70  
  Purchase #5 $156.54   13.236%   $177.2596   $177.26   $177.25   $177.30  
  Purchase #6 $77.58   13.334%   $87.9245   $87.92   $87.90   $87.90  
  Purchase #7 $201.25   13.447%   $228.3121   $228.31   $228.30   $228.30  
  7 purchase totals = $1,169.10       $1,294.1945   $1,294.18   $1,294.15   $1,294.20