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 $234.67   8.219%   $253.9575   $253.96   $253.95   $254.00  
  Purchase #2 $229.75   10.127%   $253.0168   $253.02   $253.00   $253.00  
  Purchase #3 $48.98   13.685%   $55.6829   $55.68   $55.70   $55.70  
  Purchase #4 $152.86   5.229%   $160.853   $160.85   $160.85   $160.90  
  Purchase #5 $202.97   13.702%   $230.7809   $230.78   $230.80   $230.80  
  Purchase #6 $149.95   10.662%   $165.9377   $165.94   $165.95   $165.90  
  Purchase #7 $168.90   11.260%   $187.9181   $187.92   $187.90   $187.90  
  7 purchase totals = $1,188.08       $1,308.1469   $1,308.15   $1,308.15   $1,308.20