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 $209.75   6.744%   $223.8955   $223.90   $223.90   $223.90  
  Purchase #2 $43.33   10.627%   $47.9347   $47.93   $47.95   $47.90  
  Purchase #3 $220.30   9.546%   $241.3298   $241.33   $241.35   $241.30  
  Purchase #4 $246.26   4.365%   $257.0092   $257.01   $257.00   $257.00  
  Purchase #5 $95.80   13.715%   $108.939   $108.94   $108.95   $108.90  
  Purchase #6 $80.49   4.411%   $84.0404   $84.04   $84.05   $84.00  
  Purchase #7 $45.95   6.851%   $49.098   $49.10   $49.10   $49.10  
  7 purchase totals = $941.88       $1,012.2466   $1,012.25   $1,012.30   $1,012.10