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 $95.56   6.310%   $101.5898   $101.59   $101.60   $101.60  
  Purchase #2 $187.91   12.524%   $211.4438   $211.44   $211.45   $211.40  
  Purchase #3 $178.61   13.272%   $202.3151   $202.32   $202.30   $202.30  
  Purchase #4 $95.29   12.200%   $106.9154   $106.92   $106.90   $106.90  
  Purchase #5 $47.82   11.262%   $53.2055   $53.21   $53.20   $53.20  
  Purchase #6 $142.52   8.748%   $154.9876   $154.99   $155.00   $155.00  
  Purchase #7 $209.64   3.371%   $216.707   $216.71   $216.70   $216.70  
  7 purchase totals = $957.35       $1,047.1642   $1,047.18   $1,047.15   $1,047.10