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 $57.81   5.638%   $61.0693   $61.07   $61.05   $61.10  
  Purchase #2 $219.48   12.179%   $246.2105   $246.21   $246.20   $246.20  
  Purchase #3 $130.43   10.213%   $143.7508   $143.75   $143.75   $143.80  
  Purchase #4 $160.39   7.287%   $172.0776   $172.08   $172.10   $172.10  
  Purchase #5 $52.86   13.239%   $59.8581   $59.86   $59.85   $59.90  
  Purchase #6 $108.33   5.444%   $114.2275   $114.23   $114.25   $114.20  
  Purchase #7 $212.98   9.181%   $232.5337   $232.53   $232.55   $232.50  
  7 purchase totals = $942.28       $1,029.7275   $1,029.73   $1,029.75   $1,029.80