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 $54.27   13.134%   $61.3978   $61.40   $61.40   $61.40  
  Purchase #2 $93.29   6.517%   $99.3697   $99.37   $99.35   $99.40  
  Purchase #3 $203.59   4.249%   $212.2405   $212.24   $212.25   $212.20  
  Purchase #4 $178.63   8.331%   $193.5117   $193.51   $193.50   $193.50  
  Purchase #5 $221.62   10.564%   $245.0319   $245.03   $245.05   $245.00  
  Purchase #6 $190.89   5.261%   $200.9327   $200.93   $200.95   $200.90  
  Purchase #7 $37.26   11.431%   $41.5192   $41.52   $41.50   $41.50  
  7 purchase totals = $979.55       $1,054.0035   $1,054.00   $1,054.00   $1,053.90