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 $127.75   5.693%   $135.0228   $135.02   $135.00   $135.00  
  Purchase #2 $68.68   9.637%   $75.2987   $75.30   $75.30   $75.30  
  Purchase #3 $220.93   9.184%   $241.2202   $241.22   $241.20   $241.20  
  Purchase #4 $83.70   6.391%   $89.0493   $89.05   $89.05   $89.00  
  Purchase #5 $165.50   4.828%   $173.4903   $173.49   $173.50   $173.50  
  Purchase #6 $245.41   11.144%   $272.7585   $272.76   $272.75   $272.80  
  Purchase #7 $65.38   12.605%   $73.6211   $73.62   $73.60   $73.60  
  7 purchase totals = $977.35       $1,060.4609   $1,060.46   $1,060.40   $1,060.40