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 $72.87   4.222%   $75.9466   $75.95   $75.95   $75.90  
  Purchase #2 $167.81   8.374%   $181.8624   $181.86   $181.85   $181.90  
  Purchase #3 $37.54   6.505%   $39.982   $39.98   $40.00   $40.00  
  Purchase #4 $38.59   13.496%   $43.7981   $43.80   $43.80   $43.80  
  Purchase #5 $196.26   12.567%   $220.924   $220.92   $220.90   $220.90  
  Purchase #6 $195.72   4.122%   $203.7876   $203.79   $203.80   $203.80  
  Purchase #7 $224.65   4.745%   $235.3096   $235.31   $235.30   $235.30  
  7 purchase totals = $933.44       $1,001.6103   $1,001.61   $1,001.60   $1,001.60