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 $234.81   12.379%   $263.8771   $263.88   $263.90   $263.90  
  Purchase #2 $96.51   8.735%   $104.9401   $104.94   $104.95   $104.90  
  Purchase #3 $137.83   10.867%   $152.808   $152.81   $152.80   $152.80  
  Purchase #4 $38.43   3.391%   $39.7332   $39.73   $39.75   $39.70  
  Purchase #5 $118.62   13.576%   $134.7239   $134.72   $134.70   $134.70  
  Purchase #6 $240.80   4.263%   $251.0653   $251.07   $251.05   $251.10  
  Purchase #7 $106.38   6.850%   $113.667   $113.67   $113.65   $113.70  
  7 purchase totals = $973.38       $1,060.8146   $1,060.82   $1,060.80   $1,060.80