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 $62.70   9.803%   $68.8465   $68.85   $68.85   $68.80  
  Purchase #2 $64.85   7.391%   $69.6431   $69.64   $69.65   $69.60  
  Purchase #3 $170.81   4.846%   $179.0875   $179.09   $179.10   $179.10  
  Purchase #4 $216.32   13.503%   $245.5297   $245.53   $245.55   $245.50  
  Purchase #5 $167.31   11.386%   $186.3599   $186.36   $186.35   $186.40  
  Purchase #6 $25.81   5.470%   $27.2218   $27.22   $27.20   $27.20  
  Purchase #7 $178.53   3.540%   $184.85   $184.85   $184.85   $184.90  
  7 purchase totals = $886.33       $961.5385   $961.54   $961.55   $961.50