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 $31.67   11.116%   $35.1904   $35.19   $35.20   $35.20  
  Purchase #2 $238.62   6.820%   $254.8939   $254.89   $254.90   $254.90  
  Purchase #3 $210.73   7.711%   $226.9794   $226.98   $227.00   $227.00  
  Purchase #4 $123.25   3.832%   $127.9729   $127.97   $127.95   $128.00  
  Purchase #5 $234.57   12.785%   $264.5598   $264.56   $264.55   $264.60  
  Purchase #6 $88.85   7.734%   $95.7217   $95.72   $95.70   $95.70  
  Purchase #7 $222.31   11.369%   $247.5844   $247.58   $247.60   $247.60  
  7 purchase totals = $1,150.00       $1,252.9025   $1,252.89   $1,252.90   $1,253.00