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 $194.92   4.634%   $203.9526   $203.95   $203.95   $204.00  
  Purchase #2 $126.91   10.362%   $140.0604   $140.06   $140.05   $140.10  
  Purchase #3 $234.60   9.263%   $256.331   $256.33   $256.35   $256.30  
  Purchase #4 $84.93   3.496%   $87.8992   $87.90   $87.90   $87.90  
  Purchase #5 $156.94   6.792%   $167.5994   $167.60   $167.60   $167.60  
  Purchase #6 $153.86   11.415%   $171.4231   $171.42   $171.40   $171.40  
  Purchase #7 $80.75   13.373%   $91.5487   $91.55   $91.55   $91.50  
  7 purchase totals = $1,032.91       $1,118.8144   $1,118.81   $1,118.80   $1,118.80