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 $197.41   3.171%   $203.6699   $203.67   $203.65   $203.70  
  Purchase #2 $176.54   8.830%   $192.1285   $192.13   $192.15   $192.10  
  Purchase #3 $172.94   4.681%   $181.0353   $181.04   $181.05   $181.00  
  Purchase #4 $120.49   12.671%   $135.7573   $135.76   $135.75   $135.80  
  Purchase #5 $136.60   7.759%   $147.1988   $147.20   $147.20   $147.20  
  Purchase #6 $103.57   3.414%   $107.1059   $107.11   $107.10   $107.10  
  Purchase #7 $43.86   9.668%   $48.1004   $48.10   $48.10   $48.10  
  7 purchase totals = $951.41       $1,014.9961   $1,015.01   $1,015.00   $1,015.00