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 $146.66   5.479%   $154.6955   $154.70   $154.70   $154.70  
  Purchase #2 $33.79   3.225%   $34.8797   $34.88   $34.90   $34.90  
  Purchase #3 $204.48   9.279%   $223.4537   $223.45   $223.45   $223.50  
  Purchase #4 $174.45   8.866%   $189.9167   $189.92   $189.90   $189.90  
  Purchase #5 $140.34   7.553%   $150.9399   $150.94   $150.95   $150.90  
  Purchase #6 $132.68   9.550%   $145.3509   $145.35   $145.35   $145.40  
  Purchase #7 $153.73   3.833%   $159.6225   $159.62   $159.60   $159.60  
  7 purchase totals = $986.13       $1,058.8589   $1,058.86   $1,058.85   $1,058.90