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 $244.64   11.710%   $273.2873   $273.29   $273.30   $273.30  
  Purchase #2 $193.40   9.818%   $212.388   $212.39   $212.40   $212.40  
  Purchase #3 $104.99   12.396%   $118.0046   $118.00   $118.00   $118.00  
  Purchase #4 $216.80   7.742%   $233.5847   $233.58   $233.60   $233.60  
  Purchase #5 $39.99   8.778%   $43.5003   $43.50   $43.50   $43.50  
  Purchase #6 $179.63   12.106%   $201.376   $201.38   $201.40   $201.40  
  Purchase #7 $58.30   13.172%   $65.9793   $65.98   $66.00   $66.00  
  7 purchase totals = $1,037.75       $1,148.1202   $1,148.12   $1,148.20   $1,148.20