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 $95.45   8.529%   $103.5909   $103.59   $103.60   $103.60  
  Purchase #2 $38.91   6.112%   $41.2882   $41.29   $41.30   $41.30  
  Purchase #3 $85.82   9.448%   $93.9283   $93.93   $93.95   $93.90  
  Purchase #4 $190.80   7.736%   $205.5603   $205.56   $205.55   $205.60  
  Purchase #5 $219.70   11.307%   $244.5415   $244.54   $244.55   $244.50  
  Purchase #6 $140.67   13.525%   $159.6956   $159.70   $159.70   $159.70  
  Purchase #7 $212.76   9.373%   $232.702   $232.70   $232.70   $232.70  
  7 purchase totals = $984.11       $1,081.3068   $1,081.31   $1,081.35   $1,081.30