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 $33.42   3.599%   $34.6228   $34.62   $34.60   $34.60  
  Purchase #2 $209.72   12.642%   $236.2328   $236.23   $236.25   $236.20  
  Purchase #3 $42.30   12.657%   $47.6539   $47.65   $47.65   $47.70  
  Purchase #4 $246.34   8.380%   $266.9833   $266.98   $267.00   $267.00  
  Purchase #5 $238.29   12.832%   $268.8674   $268.87   $268.85   $268.90  
  Purchase #6 $169.34   7.330%   $181.7526   $181.75   $181.75   $181.80  
  Purchase #7 $33.80   6.121%   $35.8689   $35.87   $35.85   $35.90  
  7 purchase totals = $973.21       $1,071.9817   $1,071.97   $1,071.95   $1,072.10