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 $63.34   4.701%   $66.3176   $66.32   $66.30   $66.30  
  Purchase #2 $191.92   9.431%   $210.02   $210.02   $210.00   $210.00  
  Purchase #3 $242.54   9.840%   $266.4059   $266.41   $266.40   $266.40  
  Purchase #4 $171.74   11.847%   $192.086   $192.09   $192.10   $192.10  
  Purchase #5 $65.85   4.832%   $69.0319   $69.03   $69.05   $69.00  
  Purchase #6 $145.47   11.706%   $162.4987   $162.50   $162.50   $162.50  
  Purchase #7 $106.84   10.415%   $117.9674   $117.97   $117.95   $118.00  
  7 purchase totals = $987.70       $1,084.3275   $1,084.34   $1,084.30   $1,084.30