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 $130.40   13.482%   $147.9805   $147.98   $148.00   $148.00  
  Purchase #2 $135.80   9.334%   $148.4756   $148.48   $148.50   $148.50  
  Purchase #3 $28.83   4.146%   $30.0253   $30.03   $30.05   $30.00  
  Purchase #4 $175.29   6.482%   $186.6523   $186.65   $186.65   $186.70  
  Purchase #5 $197.74   7.367%   $212.3075   $212.31   $212.30   $212.30  
  Purchase #6 $157.81   12.252%   $177.1449   $177.14   $177.15   $177.10  
  Purchase #7 $181.49   3.547%   $187.9275   $187.93   $187.95   $187.90  
  7 purchase totals = $1,007.36       $1,090.5136   $1,090.52   $1,090.60   $1,090.50