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 $184.50   5.182%   $194.0608   $194.06   $194.05   $194.10  
  Purchase #2 $64.99   6.174%   $69.0025   $69.00   $69.00   $69.00  
  Purchase #3 $183.32   12.362%   $205.982   $205.98   $206.00   $206.00  
  Purchase #4 $23.81   4.519%   $24.886   $24.89   $24.90   $24.90  
  Purchase #5 $80.44   12.130%   $90.1974   $90.20   $90.20   $90.20  
  Purchase #6 $60.99   10.695%   $67.5129   $67.51   $67.50   $67.50  
  Purchase #7 $28.38   12.245%   $31.8551   $31.86   $31.85   $31.90  
  7 purchase totals = $626.43       $683.4967   $683.50   $683.50   $683.60