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 $148.93   5.603%   $157.2745   $157.27   $157.25   $157.30  
  Purchase #2 $141.94   9.664%   $155.6571   $155.66   $155.65   $155.70  
  Purchase #3 $242.98   4.109%   $252.964   $252.96   $252.95   $253.00  
  Purchase #4 $102.67   6.627%   $109.4739   $109.47   $109.45   $109.50  
  Purchase #5 $56.80   9.742%   $62.3335   $62.33   $62.35   $62.30  
  Purchase #6 $228.66   5.435%   $241.0877   $241.09   $241.10   $241.10  
  Purchase #7 $85.31   5.484%   $89.9884   $89.99   $90.00   $90.00  
  7 purchase totals = $1,007.29       $1,068.7791   $1,068.77   $1,068.75   $1,068.90