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 $99.58   5.167%   $104.7253   $104.73   $104.75   $104.70  
  Purchase #2 $165.77   6.503%   $176.55   $176.55   $176.55   $176.60  
  Purchase #3 $34.78   6.710%   $37.1137   $37.11   $37.10   $37.10  
  Purchase #4 $138.56   5.194%   $145.7568   $145.76   $145.75   $145.80  
  Purchase #5 $245.82   7.841%   $265.0947   $265.09   $265.10   $265.10  
  Purchase #6 $122.68   3.349%   $126.7886   $126.79   $126.80   $126.80  
  Purchase #7 $140.86   3.451%   $145.7211   $145.72   $145.70   $145.70  
  7 purchase totals = $948.05       $1,001.7502   $1,001.75   $1,001.75   $1,001.80