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 $36.31   13.530%   $41.2227   $41.22   $41.20   $41.20  
  Purchase #2 $132.27   13.138%   $149.6476   $149.65   $149.65   $149.60  
  Purchase #3 $211.54   12.235%   $237.4219   $237.42   $237.40   $237.40  
  Purchase #4 $173.41   3.308%   $179.1464   $179.15   $179.15   $179.10  
  Purchase #5 $80.58   6.444%   $85.7726   $85.77   $85.75   $85.80  
  Purchase #6 $162.46   9.188%   $177.3868   $177.39   $177.40   $177.40  
  Purchase #7 $21.73   10.426%   $23.9956   $24.00   $24.00   $24.00  
  7 purchase totals = $818.30       $894.5936   $894.60   $894.55   $894.50