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 $230.89   9.596%   $253.0462   $253.05   $253.05   $253.00  
  Purchase #2 $80.92   12.455%   $90.9986   $91.00   $91.00   $91.00  
  Purchase #3 $79.44   9.564%   $87.0376   $87.04   $87.05   $87.00  
  Purchase #4 $200.75   8.836%   $218.4883   $218.49   $218.50   $218.50  
  Purchase #5 $82.43   10.820%   $91.3489   $91.35   $91.35   $91.30  
  Purchase #6 $148.84   13.395%   $168.7771   $168.78   $168.80   $168.80  
  Purchase #7 $111.26   4.654%   $116.438   $116.44   $116.45   $116.40  
  7 purchase totals = $934.53       $1,026.1347   $1,026.15   $1,026.20   $1,026.00