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 $82.96   12.594%   $93.408   $93.41   $93.40   $93.40  
  Purchase #2 $135.57   13.152%   $153.4002   $153.40   $153.40   $153.40  
  Purchase #3 $219.42   13.801%   $249.7022   $249.70   $249.70   $249.70  
  Purchase #4 $130.61   11.718%   $145.9149   $145.91   $145.90   $145.90  
  Purchase #5 $154.95   8.107%   $167.5118   $167.51   $167.50   $167.50  
  Purchase #6 $143.66   3.663%   $148.9223   $148.92   $148.90   $148.90  
  Purchase #7 $200.57   12.705%   $226.0524   $226.05   $226.05   $226.10  
  7 purchase totals = $1,067.74       $1,184.9118   $1,184.90   $1,184.85   $1,184.90