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 $53.88   5.147%   $56.6532   $56.65   $56.65   $56.70  
  Purchase #2 $120.62   3.813%   $125.2192   $125.22   $125.20   $125.20  
  Purchase #3 $99.66   13.236%   $112.851   $112.85   $112.85   $112.90  
  Purchase #4 $135.92   5.592%   $143.5206   $143.52   $143.50   $143.50  
  Purchase #5 $232.63   4.288%   $242.6052   $242.61   $242.60   $242.60  
  Purchase #6 $143.98   8.722%   $156.5379   $156.54   $156.55   $156.50  
  Purchase #7 $129.65   12.348%   $145.6592   $145.66   $145.65   $145.70  
  7 purchase totals = $916.34       $983.0463   $983.05   $983.00   $983.10