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 $5.34   8.223%   $5.7791   $5.78   $5.80   $5.80  
  Purchase #2 $171.49   10.214%   $189.006   $189.01   $189.00   $189.00  
  Purchase #3 $217.29   9.500%   $237.9326   $237.93   $237.95   $237.90  
  Purchase #4 $162.55   11.436%   $181.1392   $181.14   $181.15   $181.10  
  Purchase #5 $222.44   9.576%   $243.7409   $243.74   $243.75   $243.70  
  Purchase #6 $112.62   6.539%   $119.9842   $119.98   $120.00   $120.00  
  Purchase #7 $137.83   12.744%   $155.3951   $155.40   $155.40   $155.40  
  7 purchase totals = $1,029.56       $1,132.9771   $1,132.98   $1,133.05   $1,132.90