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 $185.52   11.621%   $207.0793   $207.08   $207.10   $207.10  
  Purchase #2 $87.93   6.566%   $93.7035   $93.70   $93.70   $93.70  
  Purchase #3 $130.57   6.280%   $138.7698   $138.77   $138.75   $138.80  
  Purchase #4 $250.99   10.558%   $277.4895   $277.49   $277.50   $277.50  
  Purchase #5 $195.28   13.427%   $221.5002   $221.50   $221.50   $221.50  
  Purchase #6 $175.72   6.163%   $186.5496   $186.55   $186.55   $186.50  
  Purchase #7 $177.55   4.202%   $185.0107   $185.01   $185.00   $185.00  
  7 purchase totals = $1,203.56       $1,310.1026   $1,310.10   $1,310.10   $1,310.10