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 $14.93   11.147%   $16.5942   $16.59   $16.60   $16.60  
  Purchase #2 $230.99   5.251%   $243.1193   $243.12   $243.10   $243.10  
  Purchase #3 $68.29   4.639%   $71.458   $71.46   $71.45   $71.50  
  Purchase #4 $169.54   13.331%   $192.1414   $192.14   $192.15   $192.10  
  Purchase #5 $175.52   13.387%   $199.0169   $199.02   $199.00   $199.00  
  Purchase #6 $205.57   4.367%   $214.5472   $214.55   $214.55   $214.50  
  Purchase #7 $232.68   11.727%   $259.9664   $259.97   $259.95   $260.00  
  7 purchase totals = $1,097.52       $1,196.8434   $1,196.85   $1,196.80   $1,196.80