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 $249.94   5.700%   $264.1866   $264.19   $264.20   $264.20  
  Purchase #2 $98.49   8.274%   $106.6391   $106.64   $106.65   $106.60  
  Purchase #3 $76.67   9.802%   $84.1852   $84.19   $84.20   $84.20  
  Purchase #4 $191.69   11.319%   $213.3874   $213.39   $213.40   $213.40  
  Purchase #5 $108.91   9.197%   $118.9265   $118.93   $118.95   $118.90  
  Purchase #6 $216.31   7.252%   $231.9968   $232.00   $232.00   $232.00  
  Purchase #7 $38.95   4.496%   $40.7012   $40.70   $40.70   $40.70  
  7 purchase totals = $980.96       $1,060.0228   $1,060.04   $1,060.10   $1,060.00