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 $77.93   8.759%   $84.7559   $84.76   $84.75   $84.80  
  Purchase #2 $201.36   5.194%   $211.8186   $211.82   $211.80   $211.80  
  Purchase #3 $200.82   7.567%   $216.016   $216.02   $216.00   $216.00  
  Purchase #4 $68.28   7.125%   $73.145   $73.15   $73.15   $73.10  
  Purchase #5 $173.37   6.427%   $184.5125   $184.51   $184.50   $184.50  
  Purchase #6 $167.41   13.191%   $189.4931   $189.49   $189.50   $189.50  
  Purchase #7 $227.41   4.284%   $237.1522   $237.15   $237.15   $237.20  
  7 purchase totals = $1,116.58       $1,196.8933   $1,196.90   $1,196.85   $1,196.90