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 $212.50   9.505%   $232.6981   $232.70   $232.70   $232.70  
  Purchase #2 $136.93   11.709%   $152.9631   $152.96   $152.95   $153.00  
  Purchase #3 $142.35   12.497%   $160.1395   $160.14   $160.15   $160.10  
  Purchase #4 $246.75   9.724%   $270.744   $270.74   $270.75   $270.70  
  Purchase #5 $10.69   9.776%   $11.7351   $11.74   $11.75   $11.70  
  Purchase #6 $173.75   13.410%   $197.0499   $197.05   $197.05   $197.00  
  Purchase #7 $21.70   3.658%   $22.4938   $22.49   $22.50   $22.50  
  7 purchase totals = $944.67       $1,047.8235   $1,047.82   $1,047.85   $1,047.70