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 $188.73   7.615%   $203.1018   $203.10   $203.10   $203.10  
  Purchase #2 $106.95   5.714%   $113.0611   $113.06   $113.05   $113.10  
  Purchase #3 $38.90   13.512%   $44.1562   $44.16   $44.15   $44.20  
  Purchase #4 $88.34   7.115%   $94.6254   $94.63   $94.65   $94.60  
  Purchase #5 $111.84   11.717%   $124.9443   $124.94   $124.95   $124.90  
  Purchase #6 $97.55   11.650%   $108.9146   $108.91   $108.90   $108.90  
  Purchase #7 $78.93   3.480%   $81.6768   $81.68   $81.70   $81.70  
  7 purchase totals = $711.24       $770.4802   $770.48   $770.50   $770.50