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 $147.52   9.645%   $161.7483   $161.75   $161.75   $161.70  
  Purchase #2 $179.62   8.703%   $195.2523   $195.25   $195.25   $195.30  
  Purchase #3 $192.69   5.760%   $203.7889   $203.79   $203.80   $203.80  
  Purchase #4 $126.32   9.656%   $138.5175   $138.52   $138.50   $138.50  
  Purchase #5 $177.79   8.643%   $193.1564   $193.16   $193.15   $193.20  
  Purchase #6 $88.69   9.214%   $96.8619   $96.86   $96.85   $96.90  
  Purchase #7 $21.47   6.790%   $22.9278   $22.93   $22.95   $22.90  
  7 purchase totals = $934.10       $1,012.2531   $1,012.26   $1,012.25   $1,012.30