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 $73.48   10.152%   $80.9397   $80.94   $80.95   $80.90  
  Purchase #2 $176.42   12.768%   $198.9453   $198.95   $198.95   $198.90  
  Purchase #3 $70.52   9.230%   $77.029   $77.03   $77.05   $77.00  
  Purchase #4 $235.63   9.199%   $257.3056   $257.31   $257.30   $257.30  
  Purchase #5 $62.60   3.872%   $65.0239   $65.02   $65.00   $65.00  
  Purchase #6 $58.54   10.570%   $64.7277   $64.73   $64.75   $64.70  
  Purchase #7 $50.86   3.560%   $52.6706   $52.67   $52.65   $52.70  
  7 purchase totals = $728.05       $796.6418   $796.65   $796.65   $796.50