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 $63.98   10.803%   $70.8918   $70.89   $70.90   $70.90  
  Purchase #2 $198.71   4.811%   $208.2699   $208.27   $208.25   $208.30  
  Purchase #3 $121.79   9.364%   $133.1944   $133.19   $133.20   $133.20  
  Purchase #4 $46.57   4.606%   $48.715   $48.72   $48.70   $48.70  
  Purchase #5 $212.52   9.154%   $231.9741   $231.97   $231.95   $232.00  
  Purchase #6 $192.29   3.227%   $198.4952   $198.50   $198.50   $198.50  
  Purchase #7 $40.25   11.767%   $44.9862   $44.99   $45.00   $45.00  
  7 purchase totals = $876.11       $936.5266   $936.53   $936.50   $936.60