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 $190.53   11.220%   $211.9075   $211.91   $211.90   $211.90  
  Purchase #2 $22.83   12.781%   $25.7479   $25.75   $25.75   $25.70  
  Purchase #3 $56.99   4.566%   $59.5922   $59.59   $59.60   $59.60  
  Purchase #4 $171.57   6.459%   $182.6517   $182.65   $182.65   $182.70  
  Purchase #5 $122.61   9.608%   $134.3904   $134.39   $134.40   $134.40  
  Purchase #6 $149.75   5.241%   $157.5984   $157.60   $157.60   $157.60  
  Purchase #7 $173.85   4.239%   $181.2195   $181.22   $181.20   $181.20  
  7 purchase totals = $888.13       $953.1076   $953.11   $953.10   $953.10