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 $210.25   11.277%   $233.9599   $233.96   $233.95   $234.00  
  Purchase #2 $134.80   12.586%   $151.7659   $151.77   $151.75   $151.80  
  Purchase #3 $169.48   5.603%   $178.976   $178.98   $179.00   $179.00  
  Purchase #4 $233.72   5.628%   $246.8738   $246.87   $246.85   $246.90  
  Purchase #5 $44.89   3.420%   $46.4252   $46.43   $46.45   $46.40  
  Purchase #6 $224.68   6.621%   $239.5561   $239.56   $239.55   $239.60  
  Purchase #7 $210.87   5.172%   $221.7762   $221.78   $221.80   $221.80  
  7 purchase totals = $1,228.69       $1,319.3331   $1,319.35   $1,319.35   $1,319.50