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 $195.55   6.442%   $208.1473   $208.15   $208.15   $208.10  
  Purchase #2 $36.52   12.327%   $41.0218   $41.02   $41.00   $41.00  
  Purchase #3 $120.76   11.584%   $134.7488   $134.75   $134.75   $134.70  
  Purchase #4 $20.49   10.413%   $22.6236   $22.62   $22.60   $22.60  
  Purchase #5 $150.73   6.439%   $160.4355   $160.44   $160.45   $160.40  
  Purchase #6 $177.35   6.170%   $188.2925   $188.29   $188.30   $188.30  
  Purchase #7 $160.98   10.658%   $178.1372   $178.14   $178.15   $178.10  
  7 purchase totals = $862.38       $933.4067   $933.41   $933.40   $933.20