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 $240.60   11.508%   $268.2882   $268.29   $268.30   $268.30  
  Purchase #2 $136.92   6.817%   $146.2538   $146.25   $146.25   $146.30  
  Purchase #3 $132.32   11.577%   $147.6387   $147.64   $147.65   $147.60  
  Purchase #4 $138.88   7.361%   $149.103   $149.10   $149.10   $149.10  
  Purchase #5 $30.89   5.290%   $32.5241   $32.52   $32.50   $32.50  
  Purchase #6 $73.53   4.829%   $77.0808   $77.08   $77.10   $77.10  
  Purchase #7 $245.42   11.202%   $272.9119   $272.91   $272.90   $272.90  
  7 purchase totals = $998.56       $1,093.8005   $1,093.79   $1,093.80   $1,093.80