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 $66.53   6.146%   $70.6189   $70.62   $70.60   $70.60  
  Purchase #2 $218.78   12.773%   $246.7248   $246.72   $246.70   $246.70  
  Purchase #3 $152.62   6.186%   $162.0611   $162.06   $162.05   $162.10  
  Purchase #4 $227.27   11.331%   $253.022   $253.02   $253.00   $253.00  
  Purchase #5 $92.60   10.115%   $101.9665   $101.97   $101.95   $102.00  
  Purchase #6 $100.88   10.228%   $111.198   $111.20   $111.20   $111.20  
  Purchase #7 $91.97   10.833%   $101.9331   $101.93   $101.95   $101.90  
  7 purchase totals = $950.65       $1,047.5244   $1,047.52   $1,047.45   $1,047.50