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 $57.55   7.816%   $62.0481   $62.05   $62.05   $62.00  
  Purchase #2 $192.97   13.608%   $219.2294   $219.23   $219.25   $219.20  
  Purchase #3 $137.27   6.220%   $145.8082   $145.81   $145.80   $145.80  
  Purchase #4 $45.31   3.370%   $46.8369   $46.84   $46.85   $46.80  
  Purchase #5 $227.40   10.297%   $250.8154   $250.82   $250.80   $250.80  
  Purchase #6 $192.85   4.836%   $202.1762   $202.18   $202.20   $202.20  
  Purchase #7 $92.61   7.398%   $99.4613   $99.46   $99.45   $99.50  
  7 purchase totals = $945.96       $1,026.3755   $1,026.39   $1,026.40   $1,026.30