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 $83.52   10.248%   $92.0791   $92.08   $92.10   $92.10  
  Purchase #2 $108.55   6.595%   $115.7089   $115.71   $115.70   $115.70  
  Purchase #3 $13.84   6.192%   $14.697   $14.70   $14.70   $14.70  
  Purchase #4 $144.65   6.321%   $153.7933   $153.79   $153.80   $153.80  
  Purchase #5 $160.51   7.563%   $172.6494   $172.65   $172.65   $172.60  
  Purchase #6 $177.56   5.256%   $186.8926   $186.89   $186.90   $186.90  
  Purchase #7 $128.36   7.293%   $137.7213   $137.72   $137.70   $137.70  
  7 purchase totals = $816.99       $873.5416   $873.54   $873.55   $873.50