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 $62.34   4.149%   $64.9265   $64.93   $64.95   $64.90  
  Purchase #2 $85.52   6.313%   $90.9189   $90.92   $90.90   $90.90  
  Purchase #3 $203.69   12.436%   $229.0209   $229.02   $229.00   $229.00  
  Purchase #4 $161.53   6.516%   $172.0553   $172.06   $172.05   $172.10  
  Purchase #5 $32.64   10.470%   $36.0574   $36.06   $36.05   $36.10  
  Purchase #6 $181.70   7.299%   $194.9623   $194.96   $194.95   $195.00  
  Purchase #7 $202.50   5.773%   $214.1903   $214.19   $214.20   $214.20  
  7 purchase totals = $929.92       $1,002.1316   $1,002.14   $1,002.10   $1,002.20