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 $220.45   6.417%   $234.5963   $234.60   $234.60   $234.60  
  Purchase #2 $96.42   13.343%   $109.2853   $109.29   $109.30   $109.30  
  Purchase #3 $168.70   12.256%   $189.3759   $189.38   $189.40   $189.40  
  Purchase #4 $238.69   11.727%   $266.6812   $266.68   $266.70   $266.70  
  Purchase #5 $149.97   4.357%   $156.5042   $156.50   $156.50   $156.50  
  Purchase #6 $12.85   9.327%   $14.0485   $14.05   $14.05   $14.00  
  Purchase #7 $68.60   6.565%   $73.1036   $73.10   $73.10   $73.10  
  7 purchase totals = $955.68       $1,043.5950   $1,043.60   $1,043.65   $1,043.60