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 $58.55   13.868%   $66.6697   $66.67   $66.65   $66.70  
  Purchase #2 $179.92   6.181%   $191.0409   $191.04   $191.05   $191.00  
  Purchase #3 $37.42   9.559%   $40.997   $41.00   $41.00   $41.00  
  Purchase #4 $130.64   7.737%   $140.7476   $140.75   $140.75   $140.70  
  Purchase #5 $170.78   10.544%   $188.787   $188.79   $188.80   $188.80  
  Purchase #6 $90.36   12.707%   $101.842   $101.84   $101.85   $101.80  
  Purchase #7 $39.96   11.276%   $44.4659   $44.47   $44.45   $44.50  
  7 purchase totals = $707.63       $774.5501   $774.56   $774.55   $774.50