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 $196.94   8.327%   $213.3392   $213.34   $213.35   $213.30  
  Purchase #2 $212.78   13.163%   $240.7882   $240.79   $240.80   $240.80  
  Purchase #3 $86.62   5.702%   $91.5591   $91.56   $91.55   $91.60  
  Purchase #4 $98.29   3.545%   $101.7744   $101.77   $101.75   $101.80  
  Purchase #5 $39.54   13.829%   $45.008   $45.01   $45.00   $45.00  
  Purchase #6 $231.61   10.835%   $256.7049   $256.70   $256.70   $256.70  
  Purchase #7 $101.33   5.174%   $106.5728   $106.57   $106.55   $106.60  
  7 purchase totals = $967.11       $1,055.7466   $1,055.74   $1,055.70   $1,055.80