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 $179.49   10.139%   $197.6885   $197.69   $197.70   $197.70  
  Purchase #2 $223.25   8.837%   $242.9786   $242.98   $243.00   $243.00  
  Purchase #3 $7.96   5.862%   $8.4266   $8.43   $8.45   $8.40  
  Purchase #4 $123.61   8.233%   $133.7868   $133.79   $133.80   $133.80  
  Purchase #5 $169.96   3.855%   $176.512   $176.51   $176.50   $176.50  
  Purchase #6 $191.52   6.497%   $203.9631   $203.96   $203.95   $204.00  
  Purchase #7 $40.73   9.198%   $44.4763   $44.48   $44.50   $44.50  
  7 purchase totals = $936.52       $1,007.8319   $1,007.84   $1,007.90   $1,007.90