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 $91.68   3.137%   $94.556   $94.56   $94.55   $94.60  
  Purchase #2 $71.75   5.336%   $75.5786   $75.58   $75.60   $75.60  
  Purchase #3 $130.38   3.841%   $135.3879   $135.39   $135.40   $135.40  
  Purchase #4 $38.86   4.689%   $40.6821   $40.68   $40.70   $40.70  
  Purchase #5 $12.97   11.220%   $14.4252   $14.43   $14.45   $14.40  
  Purchase #6 $202.89   8.179%   $219.4844   $219.48   $219.50   $219.50  
  Purchase #7 $208.37   5.539%   $219.9116   $219.91   $219.90   $219.90  
  7 purchase totals = $756.90       $800.0258   $800.03   $800.10   $800.10