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 $31.59   8.581%   $34.3007   $34.30   $34.30   $34.30  
  Purchase #2 $160.76   7.689%   $173.1208   $173.12   $173.10   $173.10  
  Purchase #3 $31.79   9.722%   $34.8806   $34.88   $34.90   $34.90  
  Purchase #4 $240.97   5.476%   $254.1655   $254.17   $254.15   $254.20  
  Purchase #5 $72.74   12.741%   $82.0078   $82.01   $82.00   $82.00  
  Purchase #6 $217.37   8.480%   $235.803   $235.80   $235.80   $235.80  
  Purchase #7 $207.66   6.703%   $221.5794   $221.58   $221.60   $221.60  
  7 purchase totals = $962.88       $1,035.8578   $1,035.86   $1,035.85   $1,035.90