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 $54.76   9.529%   $59.9781   $59.98   $60.00   $60.00  
  Purchase #2 $229.50   3.608%   $237.7804   $237.78   $237.80   $237.80  
  Purchase #3 $191.45   6.812%   $204.4916   $204.49   $204.50   $204.50  
  Purchase #4 $238.88   3.873%   $248.1318   $248.13   $248.15   $248.10  
  Purchase #5 $54.84   3.796%   $56.9217   $56.92   $56.90   $56.90  
  Purchase #6 $170.95   11.153%   $190.0161   $190.02   $190.00   $190.00  
  Purchase #7 $148.58   4.219%   $154.8486   $154.85   $154.85   $154.80  
  7 purchase totals = $1,088.96       $1,152.1683   $1,152.17   $1,152.20   $1,152.10