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 $185.65   11.584%   $207.1557   $207.16   $207.15   $207.20  
  Purchase #2 $190.85   9.611%   $209.1926   $209.19   $209.20   $209.20  
  Purchase #3 $58.45   13.430%   $66.2998   $66.30   $66.30   $66.30  
  Purchase #4 $173.34   4.760%   $181.591   $181.59   $181.60   $181.60  
  Purchase #5 $86.79   7.599%   $93.3852   $93.39   $93.40   $93.40  
  Purchase #6 $185.48   13.801%   $211.0781   $211.08   $211.10   $211.10  
  Purchase #7 $31.88   13.407%   $36.1542   $36.15   $36.15   $36.20  
  7 purchase totals = $912.44       $1,004.8566   $1,004.86   $1,004.90   $1,005.00