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 $85.67   10.632%   $94.7784   $94.78   $94.80   $94.80  
  Purchase #2 $81.46   11.690%   $90.9827   $90.98   $91.00   $91.00  
  Purchase #3 $49.47   6.449%   $52.6603   $52.66   $52.65   $52.70  
  Purchase #4 $94.49   13.720%   $107.454   $107.45   $107.45   $107.50  
  Purchase #5 $156.47   4.375%   $163.3156   $163.32   $163.30   $163.30  
  Purchase #6 $153.64   9.396%   $168.076   $168.08   $168.10   $168.10  
  Purchase #7 $80.77   5.586%   $85.2818   $85.28   $85.30   $85.30  
  7 purchase totals = $701.97       $762.5488   $762.55   $762.60   $762.70