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 $71.62   8.448%   $77.6705   $77.67   $77.65   $77.70  
  Purchase #2 $182.67   13.538%   $207.3999   $207.40   $207.40   $207.40  
  Purchase #3 $111.95   4.744%   $117.2609   $117.26   $117.25   $117.30  
  Purchase #4 $119.89   13.222%   $135.7419   $135.74   $135.75   $135.70  
  Purchase #5 $238.79   7.197%   $255.9757   $255.98   $256.00   $256.00  
  Purchase #6 $185.73   12.696%   $209.3103   $209.31   $209.30   $209.30  
  Purchase #7 $241.40   8.803%   $262.6504   $262.65   $262.65   $262.70  
  7 purchase totals = $1,152.05       $1,266.0096   $1,266.01   $1,266.00   $1,266.10