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 $219.47   12.641%   $247.2132   $247.21   $247.20   $247.20  
  Purchase #2 $189.64   6.694%   $202.3345   $202.33   $202.35   $202.30  
  Purchase #3 $32.45   8.161%   $35.0982   $35.10   $35.10   $35.10  
  Purchase #4 $159.90   5.825%   $169.2142   $169.21   $169.20   $169.20  
  Purchase #5 $71.50   11.595%   $79.7904   $79.79   $79.80   $79.80  
  Purchase #6 $230.96   13.741%   $262.6962   $262.70   $262.70   $262.70  
  Purchase #7 $58.79   7.753%   $63.348   $63.35   $63.35   $63.30  
  7 purchase totals = $962.71       $1,059.6947   $1,059.69   $1,059.70   $1,059.60