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 $228.68   3.797%   $237.363   $237.36   $237.35   $237.40  
  Purchase #2 $113.98   4.437%   $119.0373   $119.04   $119.05   $119.00  
  Purchase #3 $127.97   10.552%   $141.4734   $141.47   $141.45   $141.50  
  Purchase #4 $184.92   4.819%   $193.8313   $193.83   $193.85   $193.80  
  Purchase #5 $168.96   4.737%   $176.9636   $176.96   $176.95   $177.00  
  Purchase #6 $72.69   10.768%   $80.5173   $80.52   $80.50   $80.50  
  Purchase #7 $211.72   12.309%   $237.7806   $237.78   $237.80   $237.80  
  7 purchase totals = $1,108.92       $1,186.9665   $1,186.96   $1,186.95   $1,187.00