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 $245.36   8.813%   $266.9836   $266.98   $267.00   $267.00  
  Purchase #2 $187.94   10.140%   $206.9971   $207.00   $207.00   $207.00  
  Purchase #3 $54.39   7.434%   $58.4334   $58.43   $58.45   $58.40  
  Purchase #4 $160.56   5.539%   $169.4534   $169.45   $169.45   $169.50  
  Purchase #5 $152.75   11.656%   $170.5545   $170.55   $170.55   $170.60  
  Purchase #6 $238.85   7.305%   $256.298   $256.30   $256.30   $256.30  
  Purchase #7 $81.79   10.180%   $90.1162   $90.12   $90.10   $90.10  
  7 purchase totals = $1,121.64       $1,218.8362   $1,218.83   $1,218.85   $1,218.90