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 $24.80   8.722%   $26.9631   $26.96   $26.95   $27.00  
  Purchase #2 $65.89   3.118%   $67.9445   $67.94   $67.95   $67.90  
  Purchase #3 $186.95   12.838%   $210.9506   $210.95   $210.95   $211.00  
  Purchase #4 $240.36   6.362%   $255.6517   $255.65   $255.65   $255.70  
  Purchase #5 $117.61   7.113%   $125.9756   $125.98   $126.00   $126.00  
  Purchase #6 $241.91   8.843%   $263.3021   $263.30   $263.30   $263.30  
  Purchase #7 $65.72   13.352%   $74.4949   $74.49   $74.50   $74.50  
  7 purchase totals = $943.24       $1,025.2825   $1,025.27   $1,025.30   $1,025.40