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 $194.76   4.654%   $203.8241   $203.82   $203.80   $203.80  
  Purchase #2 $8.44   6.740%   $9.0089   $9.01   $9.00   $9.00  
  Purchase #3 $53.97   11.201%   $60.0152   $60.02   $60.00   $60.00  
  Purchase #4 $202.79   3.107%   $209.0907   $209.09   $209.10   $209.10  
  Purchase #5 $143.57   6.713%   $153.2079   $153.21   $153.20   $153.20  
  Purchase #6 $178.76   12.423%   $200.9674   $200.97   $200.95   $201.00  
  Purchase #7 $147.74   13.597%   $167.8282   $167.83   $167.85   $167.80  
  7 purchase totals = $930.03       $1,003.9424   $1,003.95   $1,003.90   $1,003.90