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 $88.57   9.306%   $96.8123   $96.81   $96.80   $96.80  
  Purchase #2 $61.43   8.498%   $66.6503   $66.65   $66.65   $66.70  
  Purchase #3 $228.87   13.608%   $260.0146   $260.01   $260.00   $260.00  
  Purchase #4 $216.33   13.497%   $245.5281   $245.53   $245.55   $245.50  
  Purchase #5 $164.50   11.461%   $183.3533   $183.35   $183.35   $183.40  
  Purchase #6 $23.89   7.229%   $25.617   $25.62   $25.60   $25.60  
  Purchase #7 $210.62   11.320%   $234.4622   $234.46   $234.45   $234.50  
  7 purchase totals = $994.21       $1,112.4378   $1,112.43   $1,112.40   $1,112.50