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 $26.96   7.649%   $29.0222   $29.02   $29.00   $29.00  
  Purchase #2 $170.43   6.302%   $181.1705   $181.17   $181.15   $181.20  
  Purchase #3 $153.86   6.385%   $163.684   $163.68   $163.70   $163.70  
  Purchase #4 $234.84   9.399%   $256.9126   $256.91   $256.90   $256.90  
  Purchase #5 $206.56   6.218%   $219.4039   $219.40   $219.40   $219.40  
  Purchase #6 $167.97   8.852%   $182.8387   $182.84   $182.85   $182.80  
  Purchase #7 $27.59   9.696%   $30.2651   $30.27   $30.25   $30.30  
  7 purchase totals = $988.21       $1,063.2970   $1,063.29   $1,063.25   $1,063.30