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 $168.93   10.829%   $187.2234   $187.22   $187.20   $187.20  
  Purchase #2 $191.78   6.209%   $203.6876   $203.69   $203.70   $203.70  
  Purchase #3 $233.28   9.213%   $254.7721   $254.77   $254.75   $254.80  
  Purchase #4 $68.96   4.302%   $71.9267   $71.93   $71.95   $71.90  
  Purchase #5 $219.38   6.285%   $233.168   $233.17   $233.15   $233.20  
  Purchase #6 $10.56   11.624%   $11.7875   $11.79   $11.80   $11.80  
  Purchase #7 $81.97   6.612%   $87.3899   $87.39   $87.40   $87.40  
  7 purchase totals = $974.86       $1,049.9552   $1,049.96   $1,049.95   $1,050.00