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 $61.62   13.414%   $69.8857   $69.89   $69.90   $69.90  
  Purchase #2 $40.73   10.554%   $45.0286   $45.03   $45.05   $45.00  
  Purchase #3 $236.57   13.287%   $268.0031   $268.00   $268.00   $268.00  
  Purchase #4 $208.52   9.454%   $228.2335   $228.23   $228.25   $228.20  
  Purchase #5 $37.71   4.149%   $39.2746   $39.27   $39.25   $39.30  
  Purchase #6 $242.35   13.598%   $275.3048   $275.30   $275.30   $275.30  
  Purchase #7 $24.57   3.362%   $25.396   $25.40   $25.40   $25.40  
  7 purchase totals = $852.07       $951.1263   $951.12   $951.15   $951.10