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 $56.55   6.748%   $60.366   $60.37   $60.35   $60.40  
  Purchase #2 $123.99   13.813%   $141.1167   $141.12   $141.10   $141.10  
  Purchase #3 $238.86   13.290%   $270.6045   $270.60   $270.60   $270.60  
  Purchase #4 $235.87   4.657%   $246.8545   $246.85   $246.85   $246.90  
  Purchase #5 $74.35   8.171%   $80.4251   $80.43   $80.45   $80.40  
  Purchase #6 $106.61   13.823%   $121.3467   $121.35   $121.35   $121.30  
  Purchase #7 $38.93   10.732%   $43.108   $43.11   $43.10   $43.10  
  7 purchase totals = $875.16       $963.8215   $963.83   $963.80   $963.80