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 $62.52   11.822%   $69.9111   $69.91   $69.90   $69.90  
  Purchase #2 $182.68   10.856%   $202.5117   $202.51   $202.50   $202.50  
  Purchase #3 $181.32   10.771%   $200.85   $200.85   $200.85   $200.90  
  Purchase #4 $172.64   6.352%   $183.6061   $183.61   $183.60   $183.60  
  Purchase #5 $230.74   11.400%   $257.0444   $257.04   $257.05   $257.00  
  Purchase #6 $61.29   5.786%   $64.8362   $64.84   $64.85   $64.80  
  Purchase #7 $163.29   3.818%   $169.5244   $169.52   $169.50   $169.50  
  7 purchase totals = $1,054.48       $1,148.2839   $1,148.28   $1,148.25   $1,148.20