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 $181.34   12.781%   $204.5171   $204.52   $204.50   $204.50  
  Purchase #2 $56.61   9.581%   $62.0338   $62.03   $62.05   $62.00  
  Purchase #3 $240.76   6.821%   $257.1822   $257.18   $257.20   $257.20  
  Purchase #4 $183.53   7.345%   $197.0103   $197.01   $197.00   $197.00  
  Purchase #5 $222.27   7.463%   $238.858   $238.86   $238.85   $238.90  
  Purchase #6 $130.94   12.833%   $147.7435   $147.74   $147.75   $147.70  
  Purchase #7 $80.72   3.154%   $83.2659   $83.27   $83.25   $83.30  
  7 purchase totals = $1,096.17       $1,190.6108   $1,190.61   $1,190.60   $1,190.60