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 $218.51   6.615%   $232.9644   $232.96   $232.95   $233.00  
  Purchase #2 $65.26   7.243%   $69.9868   $69.99   $70.00   $70.00  
  Purchase #3 $79.69   6.400%   $84.7902   $84.79   $84.80   $84.80  
  Purchase #4 $133.54   3.804%   $138.6199   $138.62   $138.60   $138.60  
  Purchase #5 $202.55   9.548%   $221.8895   $221.89   $221.90   $221.90  
  Purchase #6 $110.33   5.222%   $116.0914   $116.09   $116.10   $116.10  
  Purchase #7 $72.93   9.714%   $80.0144   $80.01   $80.00   $80.00  
  7 purchase totals = $882.81       $944.3566   $944.35   $944.35   $944.40