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 $205.60   13.213%   $232.7659   $232.77   $232.75   $232.80  
  Purchase #2 $163.98   10.651%   $181.4455   $181.45   $181.45   $181.40  
  Purchase #3 $85.83   12.433%   $96.5012   $96.50   $96.50   $96.50  
  Purchase #4 $177.72   8.809%   $193.3754   $193.38   $193.40   $193.40  
  Purchase #5 $227.29   12.696%   $256.1467   $256.15   $256.15   $256.10  
  Purchase #6 $56.97   8.807%   $61.9873   $61.99   $62.00   $62.00  
  Purchase #7 $223.40   8.717%   $242.8738   $242.87   $242.85   $242.90  
  7 purchase totals = $1,140.79       $1,265.0958   $1,265.11   $1,265.10   $1,265.10