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 $204.52   12.761%   $230.6188   $230.62   $230.60   $230.60  
  Purchase #2 $163.73   11.673%   $182.8422   $182.84   $182.85   $182.80  
  Purchase #3 $93.92   13.463%   $106.5644   $106.56   $106.55   $106.60  
  Purchase #4 $74.78   9.270%   $81.7121   $81.71   $81.70   $81.70  
  Purchase #5 $249.82   4.241%   $260.4149   $260.41   $260.40   $260.40  
  Purchase #6 $211.30   6.823%   $225.717   $225.72   $225.70   $225.70  
  Purchase #7 $201.48   3.312%   $208.153   $208.15   $208.15   $208.20  
  7 purchase totals = $1,199.55       $1,296.0224   $1,296.01   $1,295.95   $1,296.00