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 $204.93   10.629%   $226.712   $226.71   $226.70   $226.70  
  Purchase #2 $54.46   11.325%   $60.6276   $60.63   $60.65   $60.60  
  Purchase #3 $52.64   11.850%   $58.8778   $58.88   $58.90   $58.90  
  Purchase #4 $36.93   12.705%   $41.622   $41.62   $41.60   $41.60  
  Purchase #5 $108.74   8.738%   $118.2417   $118.24   $118.25   $118.20  
  Purchase #6 $162.71   7.261%   $174.5244   $174.52   $174.50   $174.50  
  Purchase #7 $11.27   4.120%   $11.7343   $11.73   $11.75   $11.70  
  7 purchase totals = $631.68       $692.3398   $692.33   $692.35   $692.20