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 $84.78   13.627%   $96.333   $96.33   $96.35   $96.30  
  Purchase #2 $186.53   13.447%   $211.6127   $211.61   $211.60   $211.60  
  Purchase #3 $145.87   3.766%   $151.3635   $151.36   $151.35   $151.40  
  Purchase #4 $132.52   4.729%   $138.7869   $138.79   $138.80   $138.80  
  Purchase #5 $208.40   13.813%   $237.1863   $237.19   $237.20   $237.20  
  Purchase #6 $190.58   7.692%   $205.2394   $205.24   $205.25   $205.20  
  Purchase #7 $33.31   11.847%   $37.2562   $37.26   $37.25   $37.30  
  7 purchase totals = $981.99       $1,077.7780   $1,077.78   $1,077.80   $1,077.80