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 $86.55   6.307%   $92.0087   $92.01   $92.00   $92.00  
  Purchase #2 $132.45   13.288%   $150.05   $150.05   $150.05   $150.10  
  Purchase #3 $33.49   9.330%   $36.6146   $36.61   $36.60   $36.60  
  Purchase #4 $188.52   8.144%   $203.8731   $203.87   $203.85   $203.90  
  Purchase #5 $192.30   10.480%   $212.453   $212.45   $212.45   $212.50  
  Purchase #6 $220.43   8.604%   $239.3958   $239.40   $239.40   $239.40  
  Purchase #7 $202.66   11.463%   $225.8909   $225.89   $225.90   $225.90  
  7 purchase totals = $1,056.40       $1,160.2861   $1,160.28   $1,160.25   $1,160.40