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 $54.67   8.245%   $59.1775   $59.18   $59.20   $59.20  
  Purchase #2 $188.43   7.640%   $202.8261   $202.83   $202.85   $202.80  
  Purchase #3 $213.80   13.325%   $242.2889   $242.29   $242.30   $242.30  
  Purchase #4 $46.26   8.832%   $50.3457   $50.35   $50.35   $50.30  
  Purchase #5 $196.65   12.807%   $221.835   $221.84   $221.85   $221.80  
  Purchase #6 $6.76   11.103%   $7.5106   $7.51   $7.50   $7.50  
  Purchase #7 $187.72   12.596%   $211.3652   $211.37   $211.35   $211.40  
  7 purchase totals = $894.29       $995.3490   $995.37   $995.40   $995.30