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 $97.63   3.802%   $101.3419   $101.34   $101.35   $101.30  
  Purchase #2 $246.51   9.766%   $270.5842   $270.58   $270.60   $270.60  
  Purchase #3 $98.61   7.465%   $105.9712   $105.97   $105.95   $106.00  
  Purchase #4 $48.91   6.434%   $52.0569   $52.06   $52.05   $52.10  
  Purchase #5 $148.85   5.811%   $157.4997   $157.50   $157.50   $157.50  
  Purchase #6 $181.67   6.143%   $192.83   $192.83   $192.85   $192.80  
  Purchase #7 $154.74   11.492%   $172.5227   $172.52   $172.50   $172.50  
  7 purchase totals = $976.92       $1,052.8066   $1,052.80   $1,052.80   $1,052.80