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 $206.92   3.789%   $214.7602   $214.76   $214.75   $214.80  
  Purchase #2 $44.83   9.804%   $49.2251   $49.23   $49.25   $49.20  
  Purchase #3 $148.52   13.862%   $169.1078   $169.11   $169.10   $169.10  
  Purchase #4 $29.56   10.539%   $32.6753   $32.68   $32.70   $32.70  
  Purchase #5 $152.39   3.218%   $157.2939   $157.29   $157.30   $157.30  
  Purchase #6 $138.57   5.240%   $145.8311   $145.83   $145.85   $145.80  
  Purchase #7 $243.95   4.628%   $255.24   $255.24   $255.25   $255.20  
  7 purchase totals = $964.74       $1,024.1334   $1,024.14   $1,024.20   $1,024.10