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 $70.80   8.713%   $76.9688   $76.97   $76.95   $77.00  
  Purchase #2 $214.32   6.245%   $227.7043   $227.70   $227.70   $227.70  
  Purchase #3 $22.60   10.265%   $24.9199   $24.92   $24.90   $24.90  
  Purchase #4 $161.85   6.229%   $171.9316   $171.93   $171.95   $171.90  
  Purchase #5 $44.29   4.594%   $46.3247   $46.32   $46.30   $46.30  
  Purchase #6 $211.44   4.814%   $221.6187   $221.62   $221.60   $221.60  
  Purchase #7 $151.37   13.311%   $171.5189   $171.52   $171.50   $171.50  
  7 purchase totals = $876.67       $940.9869   $940.98   $940.90   $940.90