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 $241.74   4.802%   $253.3484   $253.35   $253.35   $253.30  
  Purchase #2 $24.29   4.381%   $25.3541   $25.35   $25.35   $25.40  
  Purchase #3 $61.98   8.222%   $67.076   $67.08   $67.10   $67.10  
  Purchase #4 $140.74   13.813%   $160.1804   $160.18   $160.20   $160.20  
  Purchase #5 $30.70   4.705%   $32.1444   $32.14   $32.15   $32.10  
  Purchase #6 $25.39   5.328%   $26.7428   $26.74   $26.75   $26.70  
  Purchase #7 $164.52   13.302%   $186.4045   $186.40   $186.40   $186.40  
  7 purchase totals = $689.36       $751.2506   $751.24   $751.30   $751.20