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 $236.80   7.671%   $254.9649   $254.96   $254.95   $255.00  
  Purchase #2 $130.78   10.348%   $144.3131   $144.31   $144.30   $144.30  
  Purchase #3 $82.64   11.314%   $91.9899   $91.99   $92.00   $92.00  
  Purchase #4 $147.64   12.282%   $165.7731   $165.77   $165.75   $165.80  
  Purchase #5 $133.81   12.372%   $150.365   $150.37   $150.35   $150.40  
  Purchase #6 $154.92   13.472%   $175.7908   $175.79   $175.80   $175.80  
  Purchase #7 $127.75   3.386%   $132.0756   $132.08   $132.10   $132.10  
  7 purchase totals = $1,014.34       $1,115.2724   $1,115.27   $1,115.25   $1,115.40