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 $68.93   7.672%   $74.2183   $74.22   $74.20   $74.20  
  Purchase #2 $77.37   8.140%   $83.6679   $83.67   $83.65   $83.70  
  Purchase #3 $226.65   3.751%   $235.1516   $235.15   $235.15   $235.20  
  Purchase #4 $239.40   10.547%   $264.6495   $264.65   $264.65   $264.60  
  Purchase #5 $104.88   3.591%   $108.6462   $108.65   $108.65   $108.60  
  Purchase #6 $108.41   13.112%   $122.6247   $122.62   $122.60   $122.60  
  Purchase #7 $246.39   9.297%   $269.2969   $269.30   $269.30   $269.30  
  7 purchase totals = $1,072.03       $1,158.2551   $1,158.26   $1,158.20   $1,158.20