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 $82.53   13.430%   $93.6138   $93.61   $93.60   $93.60  
  Purchase #2 $22.90   3.368%   $23.6713   $23.67   $23.65   $23.70  
  Purchase #3 $142.83   7.132%   $153.0166   $153.02   $153.00   $153.00  
  Purchase #4 $128.80   11.252%   $143.2926   $143.29   $143.30   $143.30  
  Purchase #5 $73.26   4.106%   $76.2681   $76.27   $76.25   $76.30  
  Purchase #6 $218.68   12.874%   $246.8329   $246.83   $246.85   $246.80  
  Purchase #7 $28.52   11.152%   $31.7006   $31.70   $31.70   $31.70  
  7 purchase totals = $697.52       $768.3959   $768.39   $768.35   $768.40