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 $24.48   8.314%   $26.5153   $26.52   $26.50   $26.50  
  Purchase #2 $97.29   4.479%   $101.6476   $101.65   $101.65   $101.60  
  Purchase #3 $232.26   5.814%   $245.7636   $245.76   $245.75   $245.80  
  Purchase #4 $189.51   6.148%   $201.1611   $201.16   $201.15   $201.20  
  Purchase #5 $41.35   10.465%   $45.6773   $45.68   $45.70   $45.70  
  Purchase #6 $124.32   7.780%   $133.9921   $133.99   $134.00   $134.00  
  Purchase #7 $49.44   9.810%   $54.2901   $54.29   $54.30   $54.30  
  7 purchase totals = $758.65       $809.0471   $809.05   $809.05   $809.10