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 $91.50   12.137%   $102.6054   $102.61   $102.60   $102.60  
  Purchase #2 $115.56   5.809%   $122.2729   $122.27   $122.25   $122.30  
  Purchase #3 $243.27   4.469%   $254.1417   $254.14   $254.15   $254.10  
  Purchase #4 $184.40   5.565%   $194.6619   $194.66   $194.65   $194.70  
  Purchase #5 $94.92   3.241%   $97.9964   $98.00   $98.00   $98.00  
  Purchase #6 $70.26   4.668%   $73.5397   $73.54   $73.55   $73.50  
  Purchase #7 $229.58   11.340%   $255.6144   $255.61   $255.60   $255.60  
  7 purchase totals = $1,029.49       $1,100.8324   $1,100.83   $1,100.80   $1,100.80