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 $66.57   10.495%   $73.5565   $73.56   $73.55   $73.60  
  Purchase #2 $118.90   12.729%   $134.0348   $134.03   $134.05   $134.00  
  Purchase #3 $147.50   10.715%   $163.3046   $163.30   $163.30   $163.30  
  Purchase #4 $81.62   5.252%   $85.9067   $85.91   $85.90   $85.90  
  Purchase #5 $160.45   4.349%   $167.428   $167.43   $167.45   $167.40  
  Purchase #6 $221.32   3.596%   $229.2787   $229.28   $229.30   $229.30  
  Purchase #7 $161.46   12.240%   $181.2227   $181.22   $181.20   $181.20  
  7 purchase totals = $957.82       $1,034.7320   $1,034.73   $1,034.75   $1,034.70