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 $65.98   8.220%   $71.4036   $71.40   $71.40   $71.40  
  Purchase #2 $193.69   9.227%   $211.5618   $211.56   $211.55   $211.60  
  Purchase #3 $197.56   12.319%   $221.8974   $221.90   $221.90   $221.90  
  Purchase #4 $130.88   12.585%   $147.3512   $147.35   $147.35   $147.40  
  Purchase #5 $163.75   11.729%   $182.9562   $182.96   $182.95   $183.00  
  Purchase #6 $56.64   11.483%   $63.144   $63.14   $63.15   $63.10  
  Purchase #7 $151.50   5.324%   $159.5659   $159.57   $159.55   $159.60  
  7 purchase totals = $960.00       $1,057.8801   $1,057.88   $1,057.85   $1,058.00