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 $116.52   5.689%   $123.1488   $123.15   $123.15   $123.10  
  Purchase #2 $249.50   3.346%   $257.8483   $257.85   $257.85   $257.80  
  Purchase #3 $48.29   12.522%   $54.3369   $54.34   $54.35   $54.30  
  Purchase #4 $183.87   10.343%   $202.8877   $202.89   $202.90   $202.90  
  Purchase #5 $49.73   5.463%   $52.4467   $52.45   $52.45   $52.40  
  Purchase #6 $212.44   6.852%   $226.9964   $227.00   $227.00   $227.00  
  Purchase #7 $245.51   4.815%   $257.3313   $257.33   $257.35   $257.30  
  7 purchase totals = $1,105.86       $1,174.9961   $1,175.01   $1,175.05   $1,174.80