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 $149.83   11.826%   $167.5489   $167.55   $167.55   $167.50  
  Purchase #2 $56.87   6.772%   $60.7212   $60.72   $60.70   $60.70  
  Purchase #3 $116.36   9.114%   $126.9651   $126.97   $126.95   $127.00  
  Purchase #4 $177.58   3.522%   $183.8344   $183.83   $183.85   $183.80  
  Purchase #5 $237.91   6.433%   $253.2148   $253.21   $253.20   $253.20  
  Purchase #6 $202.46   9.219%   $221.1248   $221.12   $221.10   $221.10  
  Purchase #7 $223.39   6.793%   $238.5649   $238.56   $238.55   $238.60  
  7 purchase totals = $1,164.40       $1,251.9741   $1,251.96   $1,251.90   $1,251.90