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 $60.97   12.751%   $68.7443   $68.74   $68.75   $68.70  
  Purchase #2 $192.32   10.645%   $212.7925   $212.79   $212.80   $212.80  
  Purchase #3 $105.36   4.860%   $110.4805   $110.48   $110.50   $110.50  
  Purchase #4 $172.92   6.821%   $184.7149   $184.71   $184.70   $184.70  
  Purchase #5 $140.62   7.772%   $151.549   $151.55   $151.55   $151.50  
  Purchase #6 $166.50   10.228%   $183.5296   $183.53   $183.55   $183.50  
  Purchase #7 $128.66   12.731%   $145.0397   $145.04   $145.05   $145.00  
  7 purchase totals = $967.35       $1,056.8505   $1,056.84   $1,056.90   $1,056.70