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 $88.48   8.452%   $95.9583   $95.96   $95.95   $96.00  
  Purchase #2 $94.68   12.306%   $106.3313   $106.33   $106.35   $106.30  
  Purchase #3 $116.90   10.702%   $129.4106   $129.41   $129.40   $129.40  
  Purchase #4 $35.54   11.671%   $39.6879   $39.69   $39.70   $39.70  
  Purchase #5 $68.31   7.614%   $73.5111   $73.51   $73.50   $73.50  
  Purchase #6 $134.60   7.628%   $144.8673   $144.87   $144.85   $144.90  
  Purchase #7 $111.55   6.122%   $118.3791   $118.38   $118.40   $118.40  
  7 purchase totals = $650.06       $708.1456   $708.15   $708.15   $708.20