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 $177.71   7.494%   $191.0276   $191.03   $191.05   $191.00  
  Purchase #2 $227.78   5.491%   $240.2874   $240.29   $240.30   $240.30  
  Purchase #3 $222.57   10.224%   $245.3256   $245.33   $245.35   $245.30  
  Purchase #4 $206.86   12.331%   $232.3679   $232.37   $232.35   $232.40  
  Purchase #5 $180.28   4.859%   $189.0398   $189.04   $189.05   $189.00  
  Purchase #6 $60.76   5.336%   $64.0022   $64.00   $64.00   $64.00  
  Purchase #7 $49.61   5.251%   $52.215   $52.22   $52.20   $52.20  
  7 purchase totals = $1,125.57       $1,214.2655   $1,214.28   $1,214.30   $1,214.20