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 $168.52   4.164%   $175.5372   $175.54   $175.55   $175.50  
  Purchase #2 $231.66   3.731%   $240.3032   $240.30   $240.30   $240.30  
  Purchase #3 $177.96   9.146%   $194.2362   $194.24   $194.25   $194.20  
  Purchase #4 $24.49   5.235%   $25.7721   $25.77   $25.75   $25.80  
  Purchase #5 $240.37   6.518%   $256.0373   $256.04   $256.05   $256.00  
  Purchase #6 $134.52   4.871%   $141.0725   $141.07   $141.05   $141.10  
  Purchase #7 $125.72   7.605%   $135.281   $135.28   $135.30   $135.30  
  7 purchase totals = $1,103.24       $1,168.2395   $1,168.24   $1,168.25   $1,168.20