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 $65.70   13.667%   $74.6792   $74.68   $74.70   $74.70  
  Purchase #2 $192.88   3.457%   $199.5479   $199.55   $199.55   $199.50  
  Purchase #3 $226.31   8.444%   $245.4196   $245.42   $245.40   $245.40  
  Purchase #4 $146.77   11.449%   $163.5737   $163.57   $163.55   $163.60  
  Purchase #5 $144.34   4.495%   $150.8281   $150.83   $150.85   $150.80  
  Purchase #6 $161.89   5.454%   $170.7195   $170.72   $170.70   $170.70  
  Purchase #7 $15.52   6.118%   $16.4695   $16.47   $16.45   $16.50  
  7 purchase totals = $953.41       $1,021.2375   $1,021.24   $1,021.20   $1,021.20