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 $154.42   13.329%   $175.0026   $175.00   $175.00   $175.00  
  Purchase #2 $216.84   7.290%   $232.6476   $232.65   $232.65   $232.60  
  Purchase #3 $123.59   4.550%   $129.2133   $129.21   $129.20   $129.20  
  Purchase #4 $199.45   13.336%   $226.0487   $226.05   $226.05   $226.00  
  Purchase #5 $81.97   12.199%   $91.9695   $91.97   $91.95   $92.00  
  Purchase #6 $219.70   12.380%   $246.8989   $246.90   $246.90   $246.90  
  Purchase #7 $19.99   5.284%   $21.0463   $21.05   $21.05   $21.00  
  7 purchase totals = $1,015.96       $1,122.8269   $1,122.83   $1,122.80   $1,122.70