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 $248.71   13.771%   $282.9599   $282.96   $282.95   $283.00  
  Purchase #2 $54.70   10.718%   $60.5627   $60.56   $60.55   $60.60  
  Purchase #3 $37.95   3.638%   $39.3306   $39.33   $39.35   $39.30  
  Purchase #4 $145.57   6.327%   $154.7802   $154.78   $154.80   $154.80  
  Purchase #5 $226.28   8.495%   $245.5025   $245.50   $245.50   $245.50  
  Purchase #6 $25.58   4.502%   $26.7316   $26.73   $26.75   $26.70  
  Purchase #7 $231.47   5.452%   $244.0897   $244.09   $244.10   $244.10  
  7 purchase totals = $970.26       $1,053.9572   $1,053.95   $1,054.00   $1,054.00