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 $236.29   6.357%   $251.311   $251.31   $251.30   $251.30  
  Purchase #2 $95.68   4.177%   $99.6766   $99.68   $99.70   $99.70  
  Purchase #3 $216.73   13.567%   $246.1338   $246.13   $246.15   $246.10  
  Purchase #4 $220.67   4.777%   $231.2114   $231.21   $231.20   $231.20  
  Purchase #5 $99.79   13.638%   $113.3994   $113.40   $113.40   $113.40  
  Purchase #6 $13.60   9.256%   $14.8588   $14.86   $14.85   $14.90  
  Purchase #7 $92.80   3.783%   $96.3106   $96.31   $96.30   $96.30  
  7 purchase totals = $975.56       $1,052.9016   $1,052.90   $1,052.90   $1,052.90