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 $77.41   6.766%   $82.6476   $82.65   $82.65   $82.60  
  Purchase #2 $204.83   3.781%   $212.5746   $212.57   $212.55   $212.60  
  Purchase #3 $244.54   9.581%   $267.9694   $267.97   $267.95   $268.00  
  Purchase #4 $103.55   9.530%   $113.4183   $113.42   $113.40   $113.40  
  Purchase #5 $5.32   6.684%   $5.6756   $5.68   $5.70   $5.70  
  Purchase #6 $232.48   6.236%   $246.9775   $246.98   $247.00   $247.00  
  Purchase #7 $64.56   9.252%   $70.5331   $70.53   $70.55   $70.50  
  7 purchase totals = $932.69       $999.7961   $999.80   $999.80   $999.80