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 $56.80   5.558%   $59.9569   $59.96   $59.95   $60.00  
  Purchase #2 $167.74   13.868%   $191.0022   $191.00   $191.00   $191.00  
  Purchase #3 $179.86   3.320%   $185.8314   $185.83   $185.85   $185.80  
  Purchase #4 $175.87   3.676%   $182.335   $182.34   $182.35   $182.30  
  Purchase #5 $186.26   10.338%   $205.5156   $205.52   $205.50   $205.50  
  Purchase #6 $149.82   7.588%   $161.1883   $161.19   $161.20   $161.20  
  Purchase #7 $60.51   7.674%   $65.1535   $65.15   $65.15   $65.20  
  7 purchase totals = $976.86       $1,050.9829   $1,050.99   $1,051.00   $1,051.00