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 $135.64   13.270%   $153.6394   $153.64   $153.65   $153.60  
  Purchase #2 $7.33   3.278%   $7.5703   $7.57   $7.55   $7.60  
  Purchase #3 $149.48   9.690%   $163.9646   $163.96   $163.95   $164.00  
  Purchase #4 $246.36   11.834%   $275.5142   $275.51   $275.50   $275.50  
  Purchase #5 $219.65   9.737%   $241.0373   $241.04   $241.05   $241.00  
  Purchase #6 $116.88   4.203%   $121.7925   $121.79   $121.80   $121.80  
  Purchase #7 $88.66   11.363%   $98.7344   $98.73   $98.75   $98.70  
  7 purchase totals = $964.00       $1,062.2527   $1,062.24   $1,062.25   $1,062.20