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 $148.85   9.726%   $163.3272   $163.33   $163.35   $163.30  
  Purchase #2 $191.74   4.267%   $199.9215   $199.92   $199.90   $199.90  
  Purchase #3 $143.78   5.276%   $151.3658   $151.37   $151.35   $151.40  
  Purchase #4 $177.53   5.720%   $187.6847   $187.68   $187.70   $187.70  
  Purchase #5 $61.31   6.157%   $65.0849   $65.08   $65.10   $65.10  
  Purchase #6 $170.83   12.701%   $192.5271   $192.53   $192.55   $192.50  
  Purchase #7 $48.71   12.870%   $54.979   $54.98   $55.00   $55.00  
  7 purchase totals = $942.75       $1,014.8902   $1,014.89   $1,014.95   $1,014.90