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 $104.56   5.218%   $110.0159   $110.02   $110.00   $110.00  
  Purchase #2 $98.68   6.343%   $104.9393   $104.94   $104.95   $104.90  
  Purchase #3 $7.45   9.783%   $8.1788   $8.18   $8.20   $8.20  
  Purchase #4 $243.92   9.702%   $267.5851   $267.59   $267.60   $267.60  
  Purchase #5 $50.55   6.839%   $54.0071   $54.01   $54.00   $54.00  
  Purchase #6 $213.32   13.637%   $242.4104   $242.41   $242.40   $242.40  
  Purchase #7 $207.56   5.742%   $219.4781   $219.48   $219.50   $219.50  
  7 purchase totals = $926.04       $1,006.6147   $1,006.63   $1,006.65   $1,006.60