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 $49.67   8.146%   $53.7161   $53.72   $53.70   $53.70  
  Purchase #2 $157.32   5.182%   $165.4723   $165.47   $165.45   $165.50  
  Purchase #3 $119.76   10.589%   $132.4414   $132.44   $132.45   $132.40  
  Purchase #4 $186.98   8.607%   $203.0734   $203.07   $203.05   $203.10  
  Purchase #5 $112.52   10.510%   $124.3459   $124.35   $124.35   $124.30  
  Purchase #6 $147.29   13.367%   $166.9783   $166.98   $167.00   $167.00  
  Purchase #7 $233.38   5.120%   $245.3291   $245.33   $245.35   $245.30  
  7 purchase totals = $1,006.92       $1,091.3565   $1,091.36   $1,091.35   $1,091.30