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 $233.41   9.116%   $254.6877   $254.69   $254.70   $254.70  
  Purchase #2 $225.78   7.852%   $243.5082   $243.51   $243.50   $243.50  
  Purchase #3 $216.61   8.753%   $235.5699   $235.57   $235.55   $235.60  
  Purchase #4 $248.52   4.868%   $260.618   $260.62   $260.60   $260.60  
  Purchase #5 $225.65   3.668%   $233.9268   $233.93   $233.95   $233.90  
  Purchase #6 $94.72   3.200%   $97.751   $97.75   $97.75   $97.80  
  Purchase #7 $241.60   11.125%   $268.478   $268.48   $268.50   $268.50  
  7 purchase totals = $1,486.29       $1,594.5396   $1,594.55   $1,594.55   $1,594.60