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 $187.55   7.528%   $201.6688   $201.67   $201.65   $201.70  
  Purchase #2 $62.81   12.743%   $70.8139   $70.81   $70.80   $70.80  
  Purchase #3 $70.92   12.735%   $79.9517   $79.95   $79.95   $80.00  
  Purchase #4 $181.51   7.731%   $195.5425   $195.54   $195.55   $195.50  
  Purchase #5 $35.80   6.479%   $38.1195   $38.12   $38.10   $38.10  
  Purchase #6 $219.39   12.266%   $246.3004   $246.30   $246.30   $246.30  
  Purchase #7 $45.52   11.801%   $50.8918   $50.89   $50.90   $50.90  
  7 purchase totals = $803.50       $883.2886   $883.28   $883.25   $883.30