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 $209.73   9.169%   $228.9601   $228.96   $228.95   $229.00  
  Purchase #2 $224.41   4.765%   $235.1031   $235.10   $235.10   $235.10  
  Purchase #3 $61.95   6.502%   $65.978   $65.98   $66.00   $66.00  
  Purchase #4 $198.25   6.605%   $211.3444   $211.34   $211.35   $211.30  
  Purchase #5 $36.75   7.222%   $39.4041   $39.40   $39.40   $39.40  
  Purchase #6 $171.85   9.753%   $188.6105   $188.61   $188.60   $188.60  
  Purchase #7 $232.34   12.509%   $261.4034   $261.40   $261.40   $261.40  
  7 purchase totals = $1,135.28       $1,230.8036   $1,230.79   $1,230.80   $1,230.80