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 $67.25   12.440%   $75.6159   $75.62   $75.60   $75.60  
  Purchase #2 $120.56   9.758%   $132.3242   $132.32   $132.30   $132.30  
  Purchase #3 $150.37   8.777%   $163.568   $163.57   $163.55   $163.60  
  Purchase #4 $226.87   4.581%   $237.2629   $237.26   $237.25   $237.30  
  Purchase #5 $210.42   3.693%   $218.1908   $218.19   $218.20   $218.20  
  Purchase #6 $117.75   10.284%   $129.8594   $129.86   $129.85   $129.90  
  Purchase #7 $82.98   10.528%   $91.7161   $91.72   $91.70   $91.70  
  7 purchase totals = $976.20       $1,048.5373   $1,048.54   $1,048.45   $1,048.60