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 $66.35   4.870%   $69.5812   $69.58   $69.60   $69.60  
  Purchase #2 $29.69   13.457%   $33.6854   $33.69   $33.70   $33.70  
  Purchase #3 $230.27   4.128%   $239.7755   $239.78   $239.80   $239.80  
  Purchase #4 $240.45   4.424%   $251.0875   $251.09   $251.10   $251.10  
  Purchase #5 $189.35   11.737%   $211.574   $211.57   $211.55   $211.60  
  Purchase #6 $190.33   7.862%   $205.2937   $205.29   $205.30   $205.30  
  Purchase #7 $229.57   5.639%   $242.5155   $242.52   $242.50   $242.50  
  7 purchase totals = $1,176.01       $1,253.5128   $1,253.52   $1,253.55   $1,253.60