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 $212.46   3.803%   $220.5399   $220.54   $220.55   $220.50  
  Purchase #2 $203.94   4.268%   $212.6442   $212.64   $212.65   $212.60  
  Purchase #3 $59.51   10.226%   $65.5955   $65.60   $65.60   $65.60  
  Purchase #4 $35.96   3.654%   $37.274   $37.27   $37.25   $37.30  
  Purchase #5 $56.75   7.179%   $60.8241   $60.82   $60.80   $60.80  
  Purchase #6 $163.43   6.473%   $174.0088   $174.01   $174.00   $174.00  
  Purchase #7 $208.93   7.697%   $225.0113   $225.01   $225.00   $225.00  
  7 purchase totals = $940.98       $995.8978   $995.89   $995.85   $995.80