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 $89.58   6.809%   $95.6795   $95.68   $95.70   $95.70  
  Purchase #2 $10.33   6.630%   $11.0149   $11.01   $11.00   $11.00  
  Purchase #3 $211.47   7.685%   $227.7215   $227.72   $227.70   $227.70  
  Purchase #4 $41.72   9.303%   $45.6012   $45.60   $45.60   $45.60  
  Purchase #5 $157.81   8.765%   $171.642   $171.64   $171.65   $171.60  
  Purchase #6 $50.93   9.489%   $55.7627   $55.76   $55.75   $55.80  
  Purchase #7 $225.54   4.506%   $235.7028   $235.70   $235.70   $235.70  
  7 purchase totals = $787.38       $843.1246   $843.11   $843.10   $843.10