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 $67.83   12.327%   $76.1914   $76.19   $76.20   $76.20  
  Purchase #2 $211.98   4.497%   $221.5127   $221.51   $221.50   $221.50  
  Purchase #3 $64.44   11.189%   $71.6502   $71.65   $71.65   $71.70  
  Purchase #4 $14.93   10.541%   $16.5038   $16.50   $16.50   $16.50  
  Purchase #5 $247.35   6.437%   $263.2719   $263.27   $263.25   $263.30  
  Purchase #6 $220.98   4.769%   $231.5185   $231.52   $231.50   $231.50  
  Purchase #7 $125.54   11.601%   $140.1039   $140.10   $140.10   $140.10  
  7 purchase totals = $953.05       $1,020.7524   $1,020.74   $1,020.70   $1,020.80