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 $151.76   6.458%   $161.5607   $161.56   $161.55   $161.60  
  Purchase #2 $46.38   6.196%   $49.2537   $49.25   $49.25   $49.30  
  Purchase #3 $192.64   8.637%   $209.2783   $209.28   $209.30   $209.30  
  Purchase #4 $61.60   8.432%   $66.7941   $66.79   $66.80   $66.80  
  Purchase #5 $225.49   11.542%   $251.5161   $251.52   $251.50   $251.50  
  Purchase #6 $168.95   12.791%   $190.5604   $190.56   $190.55   $190.60  
  Purchase #7 $102.36   3.797%   $106.2466   $106.25   $106.25   $106.20  
  7 purchase totals = $949.18       $1,035.2099   $1,035.21   $1,035.20   $1,035.30