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 $225.56   5.146%   $237.1673   $237.17   $237.15   $237.20  
  Purchase #2 $65.59   8.293%   $71.0294   $71.03   $71.05   $71.00  
  Purchase #3 $159.77   12.442%   $179.6486   $179.65   $179.65   $179.60  
  Purchase #4 $55.36   6.575%   $58.9999   $59.00   $59.00   $59.00  
  Purchase #5 $163.88   11.376%   $182.523   $182.52   $182.50   $182.50  
  Purchase #6 $180.67   9.767%   $198.316   $198.32   $198.30   $198.30  
  Purchase #7 $121.79   11.822%   $136.188   $136.19   $136.20   $136.20  
  7 purchase totals = $972.62       $1,063.8722   $1,063.88   $1,063.85   $1,063.80