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 $83.84   10.874%   $92.9568   $92.96   $92.95   $93.00  
  Purchase #2 $194.66   13.119%   $220.1974   $220.20   $220.20   $220.20  
  Purchase #3 $135.77   7.850%   $146.4279   $146.43   $146.45   $146.40  
  Purchase #4 $197.96   13.831%   $225.3398   $225.34   $225.35   $225.30  
  Purchase #5 $227.48   8.851%   $247.6143   $247.61   $247.60   $247.60  
  Purchase #6 $77.25   5.702%   $81.6548   $81.65   $81.65   $81.70  
  Purchase #7 $137.59   12.160%   $154.3209   $154.32   $154.30   $154.30  
  7 purchase totals = $1,054.55       $1,168.5119   $1,168.51   $1,168.50   $1,168.50