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 $52.27   11.142%   $58.0939   $58.09   $58.10   $58.10  
  Purchase #2 $172.34   5.386%   $181.6222   $181.62   $181.60   $181.60  
  Purchase #3 $214.28   3.679%   $222.1634   $222.16   $222.15   $222.20  
  Purchase #4 $202.75   4.395%   $211.6609   $211.66   $211.65   $211.70  
  Purchase #5 $194.92   9.412%   $213.2659   $213.27   $213.25   $213.30  
  Purchase #6 $65.64   12.208%   $73.6533   $73.65   $73.65   $73.70  
  Purchase #7 $96.48   10.362%   $106.4773   $106.48   $106.50   $106.50  
  7 purchase totals = $998.68       $1,066.9369   $1,066.93   $1,066.90   $1,067.10