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 $241.38   5.184%   $253.8931   $253.89   $253.90   $253.90  
  Purchase #2 $207.84   10.649%   $229.9729   $229.97   $229.95   $230.00  
  Purchase #3 $161.96   12.232%   $181.7709   $181.77   $181.75   $181.80  
  Purchase #4 $35.84   5.798%   $37.918   $37.92   $37.90   $37.90  
  Purchase #5 $183.74   6.310%   $195.334   $195.33   $195.35   $195.30  
  Purchase #6 $119.72   9.783%   $131.4322   $131.43   $131.45   $131.40  
  Purchase #7 $162.38   7.645%   $174.794   $174.79   $174.80   $174.80  
  7 purchase totals = $1,112.86       $1,205.1151   $1,205.10   $1,205.10   $1,205.10