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 $245.66   10.707%   $271.9628   $271.96   $271.95   $272.00  
  Purchase #2 $145.54   4.434%   $151.9932   $151.99   $152.00   $152.00  
  Purchase #3 $63.29   3.392%   $65.4368   $65.44   $65.45   $65.40  
  Purchase #4 $203.26   6.628%   $216.7321   $216.73   $216.75   $216.70  
  Purchase #5 $127.50   5.339%   $134.3072   $134.31   $134.30   $134.30  
  Purchase #6 $84.86   13.305%   $96.1506   $96.15   $96.15   $96.20  
  Purchase #7 $244.86   12.444%   $275.3304   $275.33   $275.35   $275.30  
  7 purchase totals = $1,114.97       $1,211.9131   $1,211.91   $1,211.95   $1,211.90