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 $42.74   13.771%   $48.6257   $48.63   $48.65   $48.60  
  Purchase #2 $216.70   7.548%   $233.0565   $233.06   $233.05   $233.10  
  Purchase #3 $212.79   8.372%   $230.6048   $230.60   $230.60   $230.60  
  Purchase #4 $82.53   9.198%   $90.1211   $90.12   $90.10   $90.10  
  Purchase #5 $147.32   10.627%   $162.9757   $162.98   $163.00   $163.00  
  Purchase #6 $53.29   3.162%   $54.975   $54.98   $55.00   $55.00  
  Purchase #7 $59.52   4.500%   $62.1984   $62.20   $62.20   $62.20  
  7 purchase totals = $814.89       $882.5572   $882.57   $882.60   $882.60