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 $53.97   9.460%   $59.0756   $59.08   $59.10   $59.10  
  Purchase #2 $143.35   6.282%   $152.3552   $152.36   $152.35   $152.40  
  Purchase #3 $76.99   11.160%   $85.5821   $85.58   $85.60   $85.60  
  Purchase #4 $238.39   7.834%   $257.0655   $257.07   $257.05   $257.10  
  Purchase #5 $189.83   6.847%   $202.8277   $202.83   $202.85   $202.80  
  Purchase #6 $54.75   3.447%   $56.6372   $56.64   $56.65   $56.60  
  Purchase #7 $25.99   12.323%   $29.1927   $29.19   $29.20   $29.20  
  7 purchase totals = $783.27       $842.7360   $842.75   $842.80   $842.80